DefensiveCarry.com AR-15 Buyer's Guide

This is a discussion on DefensiveCarry.com AR-15 Buyer's Guide within the Defensive Rifles & Shotgun Discussion forums, part of the Related Topics category; If you’ve been here for any length of time, you’ve probably seen a title including the words "Which AR?" at least a couple times every ...

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    DefensiveCarry.com AR-15 Buyer's Guide

    If you’ve been here for any length of time, you’ve probably seen a title including the words "Which AR?" at least a couple times every couple months. This is notable for a couple reasons. First, it tells us that many people are buying AR-15s, and many of those for use as a home defense tool. Second, it tells us that there is not a centrally-located knowledge base for people to look at to help them decide which rifle to purchase. It is my hope that this guide can fill that vacancy and be useful for readers on the hunt for an AR-15.

    Since this is a buyer’s guide, it will share overlap with jwise’s outstanding complete AR-15 buyer’s guide. If there are any mistakes or incorrect statements, let me know and I'll fix them. If I don't in a reasonable time frame, we have mods for a reason.



    Appendix:



    Unlike in my initial version of this, there is no planned cost-benefit analysis, example builds, or "Chart" discussion section. This is a guide for what to look for in buying an AR-15, not a shopping list; availability and price change frequently, companies come and go, and it's better to know the how's and why's than just the what's. Teach a man to fish and all that. Since this is the same intent as the infamous Chart, there is no need for a discussion here. Having said that, the References section is specifically so that I/we can dump a ton of useful links and resources there. If you have some good ones, please share. If I can't get to it, ask a mod to edit it in.

    It's my hope that this guide helps members and visitors understand how the AR-15 works and how to pick out a rifle that meets their needs in a defensive AR-15, so that regardless of changes in availability and prices they'll still know what to look for.


    -Brian
    RIP, Jeff Dorr: 1964 - July 17, 2009. You will be missed.


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    Part 1 – Introduction


    The purpose of this guide is not to argue the merits of the platform. It is not to debate handgun versus long gun use for home defense. And most of all, it is not to bicker about brands. It is the purpose of this topic to help readers determine how to select from the vast array of makes and models available a rifle that suits their home-defense needs.

    Before we actually get down to brass tacks, I need to clarify something. Everything from here forward will rest on the singular assumption that you intend to take this rifle into harm’s way, or want a rifle capable being taken into harm’s way. To use a rifle “in harm’s way” means to actively face deadly force: if your rifle fails, you or others may die. I have nothing at all against recreational shooters, but this guide is not meant to help someone buy a rifle that only comes out for a match or some weekend plinking.

    Understand that the rifle is a machine, a tool. We have expectations for how our tools ought to perform and under what conditions, and this is no less true with a rifle chosen for home defense. Because this is a tool we will be entrusting our life to, it needs to be absolutely reliable. Our goal is to eliminate the rifle as a variable in why things might go wrong. The less time spent on fixing the rifle, the more time can be put into shooting it.





    (Continue to Part 2)
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    Part 2 – Key Components


    What makes a good, reliable rifle? Some components are more critical than others in producing a reliable rifle. Broken bolts, poorly staked carrier keys, incorrect chamber specs, a weak extractor spring, the castle nut slipping off, or the wrong buffer for the gas system will all stop your rifle in a hurry. For our purposes, this means we ought to prioritize the parts actually effecting rifle function: whole bolt carrier group, the buffer assembly, and the barrel (covered in a follow-up post).



    Bolt Carrier Group

    A brief overview of what bolt-related failures look like can be found here in the 2006 NDIA Small Arms Symposium, SOPMOD Program Overview (search “bolt failure”). Generally, harsher firing schedules will wear bolts out between 3,000 and 6,000 rounds. Milder firing schedules may extend bolt life to 10,000 rounds. Additionally, Bill Alexander (Alexander Arms: Welcome to the Revolution) points out here that poorly made bolts will wear the barrel extension unevenly, potentially creating excessive headspace. Excessive headspace leads to case head separation with sub-optimal brass (not an easy malfunction to fix). Buying good bolts is a must, as is keeping good spares on-hand.

    Staking the bolt-carrier key screws correctly is one of the easiest things to do, and yet is seldom done. A gas key that comes loose in shooting will cause short-stroking, turning that fine AR-15 into a single-shot rifle. Rob at VA Arms created an excellent topic on M4C (here) showing what proper carrier key staking looks like. If your carrier key staking doesn’t look like this, it needs to. Staking tools are available from Ned Christiansen, and many reputable gunsmiths (G&R Tactical, VA Arms, etc) will do it for a small fee.

    The last part of the bolt carrier group we care about is the extractor assembly. A weak extractor in the AR-15 causes the extractor claw to slip off the rim of the cartridge. This will result in a failure to extract the spent brass from the chamber. These problems are exaggerated in a carbine-length AR-15. Crane developed an extractor upgrade kit in response to this, and since then so have several other companies. MGI’s D-ring has been extensively tested by Crane and is also a good upgrade option. For carbines, the black insert is what you’re looking for (which you’ll see in the links provided).



    Buffer Assembly

    The buffer assembly in the AR-15 is to slow down the rearward-moving bolt carrier group and eventually return it to battery. There are choices between mil-spec and commercial receiver extension tubes, a variety of buffers and action springs available, and misconceptions of how to keep the whole thing together.

    First, terminology: buffer tube and receiver extension tube are synonymous, as are buffer spring and action spring. Yes, the latter term in both examples is technically correct. No, it’s not worth worrying about.

    Mil-spec versus commercial tubes – there are more differences than just the names, and in building a fighting rifle we do have a preference. K.L. Davis describes them in detail on M4C here. Put simply, the diameter of mil-spec tubes is greater in the threading than in commercial tubes, despite the commercial tubes’ greater diameter past the threading. Why do we care? Commercial tubes will not fully engage the threading in the receiver, which can allow the tube’s threads to pull away from the receiver. No joy. It’s not a common failure, but an easily avoidable one. Get a mil-spec buffer tube. If you’re using a rifle/A1/A2 tube, you’ve nothing to worry about since they’re all the same.

    Buffers and action springs are a bit broader in scope. Everything you could ever want to know about the different buffers and what length action springs you want can be found here. I strongly recommend first running what comes with the gun. Only change something after you find your rifle short-stroking or overcycling (gas port variances between guns play a big role here). Too heavy and/or too long an action spring will cause short-stroking (bad), and too light a buffer and/or too short an action spring will cause overcycling (also bad). Over time the gas port will erode, allowing more gas into the action and changing the cycling behavior. In addition to replacing an action spring worn too short, switching to a heavier buffer might also be beneficial. Seek balance you must, young Jedi.

    The Vltor A5 buffer system is a modern upgrade that warrants discussion. To quote MilitaryMorons.com, "The A5 system provides the functionality of a collapsible stock while maintaining rifle-length buffer system reliability." It was made to address the issue of the military using various length uppers that require equally-varied buffer assemblies. Rifle-length systems are generally more consistent and reliable than carbine-length systems. Compared to the carbine buffer assembly, the A5 system uses a longer buffer tube, heavier buffer(s), and a rifle-length action spring. The A5 package maintains the rate of fire, carrier velocity, and reliability of the rifle-length A2 stock across a wide variety of uppers. "Lancelot" on AR15.com and Rob Jensen on M4C demonstrate this nicely. In any case, it's a viable option for those building their own AR-15 or looking to upgrade an existing one.

    Finally, how to keep the whole system together. If you’ve got a fixed-stock assembly, you’re again in luck. Screwing the stock in place is the most you have to do. If you have a collapsible stock, however, things change a bit because we now have a castle nut. Castle nuts are meant to prevent rotation and hold something in place, and have slots or cuts meant to be filled with material to accomplish this. That material is meant to come from the receiver end plate. An unstaked castle nut will eventually back off and come loose. Once it comes loose, so too does the stock it was holding in place. Collapsible stocks will rotate freely at this point, doing two things: annoying the hell out of you, and backing off enough to allow the rear takedown pin’s detent spring to escape. A jostle, rough bump, or similar motion is all it would take for the rear takedown pin to disappear and open your rifle up. Here is what you want to stake, courtesy of Rob from VA Arms.

    Loc-Tite is a common and very poor substitute for staking the castle nut. It’s a pain to remove if you want to swap stocks, especially if you want to reuse the same buffer tube. Staking is easy to apply, easy to remove, and receiver end plates are cheap.



    (Continue to Part 3)
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    Part 3 – The Barrel and Gas System

    The barrel has been accurately called the heart of the AR-15. It’s the single most expensive component of the rifle itself and is the part that directly influences the bullet as you send it downrange. It's sole function is to provide a reliable path through which the fired bullet will travel, but it will also be the most determining factor in how maneuverable a rifle is. Unfortunately, it is also the subject of more voodoo than any other part of the platform; this is discussed in some detail by Kino L. Davis here, from whom I'll be quoting much.

    Currently, the list of characteristics to look for in a fighting barrel is something like this:

    • Barrel length
    • Gas system
    • Barrel steel, construction, and rifling
    • Barrel contour or profile
    • Rate of twist
    • chamber


    Each of these will be discussed in detail.



    Barrel Length


    The overall length of your barrel determines both your maximum effective range and your overall weapon maneuverability. The longer a bullet can ride those expanding gases, the more velocity it will have. The longer the barrel, though, the less wieldly the rifle will be.

    Maximum effective range is highly dependent on velocity, or how fast the bullet is going when it hits something, which in turn is dependent on barrel length. Different bullets have different speeds they need to be at when hitting a target for optimal effect; M193 and M855 both require nominal velocities of 2700 feet per second (fps) to upset reliably, where the OTM Sierra bullets in the Mk262 only need to be moving 2300 fps to achieve reliable upset. Nowadays, most bullet manufacturers are nice enough to publish how fast their rounds need to be going to achieve optimal effect.

    In a 20" barrel, that 2700fps mark can be achieved out to 130 yards for M193, 120 yards for M855, and 210 yards for Mk262. Drop down to a 16" barrel, and those distances become 105, 90, and 170 yards. Shave another inch and a half to use a 14.5" barrel, and that range shrinks to 105, 105, and 145 yards. This trend continues as the barrel shortens, getting harder to achieve those optimal velocities the further you go into SBR length barrels. Fortunately, we won't be using M193 and M855 for personal defense. There are much, much better options. Barnes TSX bullets, for example, work well down to 1800 fps. The specialty Hornady and Sierra bullets, while not quite as effecient, still do well at much slower speeds than the 2700 required by the M193 and M855. With most modern self-defense rounds, we can still have 100+ yard capability from our rifles even out of short, NFA-length barrels.

    While the most likely scenario of us using an AR-15 for personal defense is within the home, we shouldn't ignore the long shots either. Look down your street and guess about how far your house is to the nearest stop sign, or how far your back yard extends beyond your house. Try the same exercise in a parking lot, estimating from your car to a couple random other points. Civilians and law enforcement alike can very easily be pressed into 25-100 yard shots, which makes those needed feet per second somewhat more important than they would be if the weapon would only be used in bad breath range.

    For most of us, a 16" or 14.5" barrel with a permanent muzzle device will be the best compromise. The 16" barrel gives a little more flexibility and lets you choose different muzzle devices, but costs you another 1.5" of overall length. Both of them spare you the headache of NFA paperwork. If you're willing to go through the process, though, an 11.5-12.5" barreled gun is probably the ideal length for maneuvering inside a home, with modern ammunition letting that SBR be effective even out to/past 100 yards.



    Gas System (warning - long read)

    Before going into this, we need to look at how the AR-15 actually works. This is good to know in general, great to know when fixing a factory gun, and should be considered mandatory to know for building your own.

    When a round is fired, an immediate pressure spike builds inside the cartridge case. The cartridge expands outward, contained by the chamber and bolt face, which hold the case in place and forces the propellant to push as the bullet is propelled down the barrel. The bullet is moving a lot faster than the bolt face due to its smaller mass, so the propellant gases expand down the barrel and push the bullet ahead of them. Remember that the gas port is a hole in the barrel designed to siphon off some of those expanding gases to cycle the action. Once the bullet passes the gas port, some of of the pressure is lost. The total pressure built up until this point is the chamber pressure, and will drop dramatically (to 12-15k PSI or so) until the bullet passes the muzzle. The moment the bullet leaves the barrel, gasses escape behind the bullet going several times faster than the bullet itself.

    During that time between the bullet passing the gas port and it leaving the barrel, a specific amount of gas was expanded into the gas port, down the gas tube, and into push the the gas piston on top of the bolt carrier. Here it will expand into that little chamber just behind the bolt. In doing so, it forces the bolt forward and the bolt carrier backward. The pressures that originally pushed back against the bolt are more or less equal (for a short time) with the pressure of the gas now behind the bolt. By now the cartridge case should have returned to its original size and the bolt will begin to turn and unlock, followed by the extractor pulling back on the case head. The rearward force against the bolt carrier group eventually overcomes the forward force on the bolt, causing it to move backwards against the inertia of the carrier's own weight, the buffer's weight, and the action spring.

    The whole time the case head is held by the bolt, the ejector has been putting pressure on one side of the case head. Because it's been held in place by the chamber, it hasn't gone anywhere. Once the bolt carrier group moves far enough back to pull the spent casing from the chamber and to the ejector port, the case no longer has counter-pressure on its right side and the ejector kicks the spent casing out.

    To quote Randall from AR15barels.com,

    We want the bullet to be out of the front of the barrel AND the pressure to have subsided enough that the case shrinks down BEFORE the bolt lugs are unlocked because when the pressure is high, the case WILL try to stay in the chamber.
    Now is the perfect time to point out that one sure sign of high pressures are the fact that the case extrudes into the ejector plunger hole on the bolt and the resulting pressure unlocks the bolt while pressures are still high.
    This extruded brass gets wiped off the end of the case head, leaving a shiney spot and the brass usually makes it's way under the extractor, later causing extraction problems we will get to in a little bit.
    Here is a graphic illustrating what happens when pressures are too high and the gas system is getting too much gas:

    Most of what I described is also described in as much, or more, detail on Randall's site. As you can see, this whole process is highly dependent on timing, hence the different weight buffers that exist to regulate said timing.

    Now we can talk about the actual gas systems used in the AR family of weapons.



    The rifle length system, a 20" barrel with the gas port located 13.2" out, is the original gas system for the M16. Adopting shorter barrels necessitated the Carbine system, with the port 7.8" out on what was originally a 10-11" barrel, then evolved into the standard 14.5" barrel we see on M4s today. The mid-length system, with its gas port 9.8" out, was developed much later primarily for 16-18" barrels.

    When we talk about the 'gas system' of a barrel, we're talking about gas port location, specifically the distance from the breach to the gas block. If you remember, chamber pressure is the total pressure exerted on the bolt and chamber in that time between the round being fired and the bullet clearing the gas port. Different gas systems result in different pressures.



    As you can see, the further out the gas port is, the lower the chamber pressure. Think about it like an explosion in a room. The smaller the room, the more the pressure builds before being allowed to expand. The larger the room, the more the gases can expand before the pressure builds. For the same reasons, chamber pressures are lower on the longer gas systems of the mid-length, intermediate (not listed), and rifle systems. This leads to fewer pressure related failures - blown primers and ruptured cartridges are prime examples.

    Now that the bullet has passed the gas port, we get to another critical point: that time between the pressure bleed off at the gas port, and when the bullet ultimately leaves the barrel. In the gas operated system of the AR-15, we call this dwell time.

    Dwell time is basically the amount of time that the bullet is past the gas port, but still in the barrel. It's a simple enough concept, but a critical one to know if you want to understand how an AR-15 works. Until that bullet passes the gas port, the AR is a single-shot rifle; the bullet must clear the gas port to allow those expanding propellants to expand into the gas port, down the gas tube, and into the gas piston on the bolt carrier. However, without the bullet blocking gas expansion down the barrel, the propellants would simply expand out the barrel instead of up into the gas port. The bullet acts as resistance to the expanding gases, forcing them to enter the gas port and operate the rifle's action while waiting for the bullet to leave the muzzle so the gases can expand out behind it.

    If dwell time is too long (a longer distance between gas port and muzzle), more gas enters the gas port and the carrier group is pushed back more harshly than is necessary. This is called overgassing, which will wear down parts quicker and produce more felt recoil in the form of a harsher recoil impulse (the actual amount of recoil doesn't change, just how it feels). It can also disrupt the timing of the bolt carrier, causing malfunctions in extraction or ejection*. If the dwell time is too short (shorter distance between gas port and muzzle), not enough gas enters the gas port and the carrier group may not be pushed back far enough to cycle the action or lock back on the last round. This is undergassing, or more commonly known as short-stroking. It's gentler on the rifle and has a softer or smoother recoil impulse, but basically gives you a single-shot rifle. What we're looking for is that 'golden mean', that sweet spot in dwell time so that our rifle is fed enough gas to function reliably but not so much that it is worn down prematurely or that the recoil becomes harsh.

    It just so happens that a few folks have done just that kind of research. Credit again goes to Randall.



    Advice time. Most people* using a 16" barrel will be best served by a mid-length gas system. Most people using a 14.5" barrel will be best served by a carbine gas system. If buying a short-barrel rifle, buy quality from the get-go: Bravo Company, Centurion Arms, Colt carbines modified by Specialized Armament, Daniel Defense, Lewis Machine & Tool, and Noveske Rifleworks. Conveniently enough, those are basically our go-to companies for most parts AR-15 related**.

    *I say "most people" because most people will not be mucking about with the guts of their rifles after buying or putting them together. There is a growing trend in using 14.5" mid-length barrel systems. Everything else being equal, they do feel differently than 14.5" carbine systems. Combined with a heavier buffer and/or modified buffer system like Vltor's A5, it is possible to create an extremely low-recoil system. Bushmaster popularized the "Dissipator", visually resembling a 16" barrel with a rifle gas system and handguards. In reality it is a carbine gas system hidden under the handguards, but the attraction of a larger grip surface, lower chamber pressures, and softer recoil has resulted in some folks toying with the gas port size to account for the abnormal dwell time. When the system works, it is awesome how smooth the weapon feels while still keeping a shorter 16" barrel. Getting it to work takes effort, though.

    ** Many companies (Bushmaster, DPMS, RRA, S&W, etc.) intentionally overgas their systems by using larger-than-normal gas ports. It lets them function on weaker ammo, but makes the stronger ammo harsher on the rifle and more prone to inducing damage or malfunctions. The simplist fix for this is using different weight buffers. Companies like Bravo Co., Daniel Defense, Noveske, and others do not have access to the TDP like Colt, but instead conduct cyclic rate testing to fine-tune their gas port sizes.



    Barrel Steel, Construction, and Rifling


    Barrel Steel

    Do you know the differences between chrome-moly 4140, 4150, and CMV? What about 410, 416, and 17-PH stainless? If you read my previous link to the M4C article by Kino Davis, you'll be ahead of the curve. If not, don't worry, I'll be quoting him a bit. Starting now, in fact.

    About 99% of barrels are made up of one a few different types of steel alloy -- of these, the choice is pretty much between Chrome-Moly steel and Stainless Steel.

    Chrome-Moly - This name is used to describe a broad family of steels, the most common in use for the AR are 4140 and 4150... the 41xx indicates the AISI-SAE numbering for Chromium-Molybdenum alloy (ergo the name Chrome-Moly), these steels are alloyed with about 0.50% to 0.95% Chromium and 0.12% to 0.30% Molybdenum. The second part of the number indicates that percentage of Carbon (in tenths of a percent). Therefor 4140 is about 0.40% Carbon and 4150 about 0.50% -- the extra carbon in 4150 makes the steel a little tougher and it resists heat better... but it is harder to work and machine.

    4150 is one of the "MilSpec" steels... another that is used in a lot of military barrels is CMV (Chrome-Moly-Vanadium) -- as the name implies, this is a chrome-moly steel (very close to 4150) with the addition of about 0.20% to 0.30% of Vanadium. CMV is reported to perform better under high heat.

    Carbon steel barrels (chrome-moly) are the bread and butter of barrel materials for the AR, chrome-moly has made great barrels for many years and will continue to do so for many more. The only real downside to carbon steels is that they are prone to rust and corrosion problems.

    Stainless Steels - We all know stainless steel, very high levels of chromium and nickel make these steels very resisitant to rust and corrosion, they are used in nearly every type of manufacturing around... the most common choices of stainless for a barrel are 410 and 416. There are a few "families" of stainless steel, but all of that is really academic to the discussion -- but 410 and 416 are Martensitic steels... simply they have lower percentages of chromium than other types of stainless steel.

    The most common stainless in use for AR barrels is 416, this steel is plentiful, not expensive and machines nearly as well as the carbon steels -- 416 is rather strong, and has decent corrosion resistance; however, it is one of the least corrosion resistant of the stainless steels. Another choice barrel makers offer is 410, it is a little tougher and more corrosion resistant, but is harder to machine.

    Grade 630 stainless, often called 17-4PH, is a great steel that offers excellent corrosion resistance and hardness. 630 is tough, but machinable, and tempers well. It is a precipitation hardened (PH) or age hardened steel and does not distort significantly during the hardening process; however, one consideration for the use of 630 is that the steel manufacturers do not recommend using it for applications that will expose it to cycling temperatures above 700 (f) -- In some cases this is not an issue, however in an AR that may see "heavy fire", 630 (17-4PH) is not a great choice.

    So which is better, CM or SS? Again, this depends on what you want/need... a few things that seem to hold true about the two are that: CM barrels may take a little longer to break in and can be more prone to copper fouling; Due to the way the metal erodes in the throat area, the acuracy of CM barrels tends to degrade at a more steady rate, where SS tends to fall off quickly towards the end of its life; The throat area of CM barrels can work harden, this makes recutting the chamber and "bumping" the barrel back difficult -- but AR barrels can not be bumped back anyway (due to the gas port); SS barrels tend to be more prone to scratching but naturally is better at resisting corrosion (over an unplated CM bore); Many barrel manufacturers do not recommend using SS in sub-zero cold; Either SS or CM is capable of the same accuracy and will have about the same service life.
    Generally speaking, barrels described as Mil-B-11595E chrome-moly vanadium steel are what we want. These should also come with chrome-lined bores and chambers for better corrosion resistance; I don't believe I've ever seen a Mil-B-11595E CMV barrel that was unlined.


    Construction and Rifling

    Once the barrel blank is made, it gets rifled before being profiled. There are several ways of accomplishing this - button rifling, broach cutting, single point cutting, hammer forging, checmical or anode/cathode etching, etc. For AR barrels, we really only care about two: button rifling and hammer forging.

    The vast majority of AR barrels are rifle buttoned. This involves pushing or pulling a rifled button through a barrel blank and forcing the rifling into the bore. There is nothing inherently wrong about the technique; it is how Colt and FN Herstal make the M4 and M16 series weapons for our own military. As long as you're buying from a good source (like one of the manufacturers listed earlier), you can enjoy a long, happy lifespan on your rifle-buttoned barrel.

    With this in mind, a number of companies have brought to market cold hammer-forged barrels. CHF barrels are generally much more durable and have significantly longer service lives, at the cost of being slightly to not-so-slightly more expensive than non hammer-forged barrels (in some cases commanding a $100 or higher premium). Excepting LMT, all of the previously-listed companies make CHF barrels; excepting Colt's, all are available commercially. I don't believe it's possible to get a Colt hammer-forged barrel - to my knowledge they're made exclusively for the C7s and C8s in use by our northern brothers.

    The type of rifling is another much-debated point that we really, honestly, truly don't need to worry about. Buy a barrel from one of the aforementioned manufacturers and you will be just fine. Type of rifling comes into play more for competition shooters going for extreme accuracy, often at long distances. Even in defending one's rural property it would be hard to find a home-defense scenario in which the type of rifling your barrel has will make or break your abiltiy to defend yourself or your loved ones.



    Barrel Contours

    Heavy rifles suck. They're slower to move around and they tire you out quicker. Given that your barrel is a long tube of steel, its profile (the external diameter and how it changes along its length) will play a pretty significant role in determing the overall weight and balance of your rifle. Case in point:

    Colt 16" HBAR: 2 pounds 3.4 ounces
    Colt 16" M4 profile barrel: 1 pound 12 ounces
    Colt 16" lightweight profile: 1 pound 6 ounces

    There are many different types of barrel contours, ranging from heavy barrel (HBAR) profiles an inch or more in diameter to lightweight and pencil barrels nearing half-that. Of the many different profiles, the government profile is the most common: thinner under the handguards, thicker past the gas block. Not because it's better than others (quite the contrary, in fact), but simply because it's what is on the M4 and M16 series carbines and rifles. Adding another 6 ounces or more to the end of the barrel is not an exercise in brilliance.

    Generally speaking, the thicker the barrel is, the more it resists changes in temperature (takes longer to heat up and cool down) and the less it will flex when fired. Thinner barrels are just the opposite, less resistant to temperature changes (heating up quicker and cooling off quicker) and more prone to flexing when fired. Flex matters a lot in accuracy shooting, and matters more the further out you get. This is when barrel heat also matters; the hotter a barrel gets, the more point of impact will shift. Inside of 100m, though, it would be very difficult to argue the point. In home-defense scenarios, it's equally hard to imagine shooting enough quickly enough to heat the barrel such that temperature resistance matters.

    Manueverability is directly influenced by barrel weight and where that weight is distributed. A 1 pound 12 ounce Noveske contoured barrel will handle much differently than a 1 pound 12 ounce M4 profile barrel simply because of where the weight is. Keep in mind that physics is pretty consistent: it doesn't matter how big or strong you are, you will always move a lighter rifle quicker than a heavier rifle. Similarly, on equivalent weight barrels, the one with the most material closest to the receiver will also be the quickest.

    Opinion: It's for this reason that I greatly prefer lightweight barrels - speed counts when a door is kicked in or window broken through and a lighter, better balanced rifle is always[i] more maneuverable than a heavier rifle with poorer balance. While there is a lot of hemming and hawing about the sacrifices made when choosing anything short of a bull-barrel, even the less-than-optimally designed M4 profile survived more than 500 rounds of full automatic fire before rupture. That's 16 or more 30-round magazines, as fast as the gunner can feed them, without lube (courtesy of NY Times and .mil.) Even if the lighter weight barrels do fail sooner, it is nearly inconceivable to require the dozen or more magazines worth of full-auto fire to protect my home and family necessary to push the barrel to failure.



    Rate of Twist

    This ratio describes the length the bullet will travel to complete one full rotation within the barrel (ex: A 1:7 barrel means the bullet travels 7" to make 1 full rotation). The original twist for the M16 was 1:14, which combined with the 55 grain M193 produced outstanding terminal effects but poor penetration and poor accuracy in cold weather. Tightening up to 1:12 vastly improved its external ballistics at the cost of its terminal ballistics (we'll go into ballistics in a later section). In the M16A2, the barrel twist tightened all the way to 1:7 to properly spin the longer tracer rounds.

    Without delving too deep, we care much more about 1:7 and 1:8 twist barrels than any others. As described by this article on PoliceOne, the biggest consumer of all small arms ammunition is the military, meaning ammunition manufacturers have been catering to the 1:7 twist for .224 bullets for a long time and have developed some great rounds for personal defense... for the 1:7. Using the excellent Sierra 77gr OTMs, Hornady 75gr T2, and several other heavier/longer bullets, the 1:9 twist barrels are inconsistent. Some of this falls on the manufacturer (RRA's 1:9 vs DPMS's 1:9); according to Giles Stock, some 1:9 barrels will run closer to 1:8 and do well with the heavier/longer ammo while some will run closer to 1:10 and do miserably with it. 1:12 twist barrels need not apply - there military specifically moved away from the 1:12 twist because it could not handle the longer bullets in the XM856 phospherous tracers. Though looser twists can't [usually] handle longer bullets, 1:7 and 1:8 twist barrels have little or no trouble shooting lighter/shorter .224 bullets.

    Technically, the 1:8 twist barrel is perfect for anything that will fit in an M16 30-round magazine. It's just harder to find because 1:7 is used by the military and works so well in general. For our purposes, the 1:7 and 1:8 are what we want in an AR barrel, with availability favoring the 1:7.

    There is some decent ammunition for 1:9 and 1:12 twist barrels, but your options are greatly reduced. Ammunition will be discussed in greater detail later.



    Chamber

    This should be a very short section: 5.56x45 NATO is the only chamber we really care about as consumers buying a rifle for personal defense. Noveske uses a modified 5.56 chamber similar to the .223 Wylde in their stainless barrels that is also fine (and well it should be, since it's designed for full-auto fire of Mk262).

    The problem with just leaving this recommendation at the previous two sentences is that many companies flat lie. What's printed on their barrels and receivers is very often not the actual chambering of the weapon: 5.56 is just as often .223 Remington. Bushmaster, DPMS, Olympic Arms, Rock River Arms, and Smith & Wesson are all guilty of this in the past and present. This is not a small deal - there is about a 20,000 psi difference between NATO and SAAMI specs for chamber pressure. The .223 Wylde chamber, a hybrid of 5.56 NATO and .223 Remington and seen most often in RRA rifles and LaRue rifles, can be fine. In theory. It has far fewer reported issues when running 5.56 ammo than using the same in .223 Remington weapons. RRA may be questionable at best, but LaRue is certainly not.

    A great comparison of reamers for the .223 Rem, 5.56 Nato, and various hybrids can be seen here. You can briefly summarize the differences like so:

    The 5.56 chamber is a sloppy military chamber with a long throat(.226 diameter and .056 long), the .223 chamber is tighter in all dimensions and has a shorter throat(.025 long), works well with varmint bullets.
    The Wylde has a generous chamber size but the throat is smaller in diameter(.224) to hold the bullet in line with the bore better , the freebore is .061 long.


    (Continue to Part 4)
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    Part 4 – Support Components


    Support components are those things that are also important to your rifle but don’t directly influence its function; things that you can take on or off at will and expect the rifle to still work the way it’s supposed to. Handguards can help with accuracy, cooling, and provide attachment points for lights and additional grips. Magazines are necessary to feed the thing. Weaponlights help you ID your target, and sights and optics help you actually hit your target. A muzzle device can make or break your game plan once the trigger is pulled. Whether slings are necessary on a home-defense long gun is debatable, but they certainly have value for law enforcement (and are typically required in carbine instruction courses).



    Handguards

    There are three main criteria people select handguards by: whether they’re free-floating, how securely they mount and can be mounted to, and weight. A “free float” handguard is one that does not contact the barrel, and thus one that does not change point of impact if the weapon is positioned against something (cover, for instance...) or if a sling is used as a firing aid. The accuracy benefit of free-floating is lost in a home-defense scenario, but law enforcement might find it advantageous to rest their rifle up on a barricade or their car without having to worry about an altered point of impact. Daniel Defense and LaRue Tactical are currently top-dogs in the AR quad-rail handguard market, but a more complete list of the different handguards can be found here. That list does not include the JP/VTAC modular handguard and the VTAC Extreme / Troy TRX Extreme handguards (the same, just slots vs holes). Newer high-quality alternatives include the Noveske NSR handguard and Giessele modular rails, which also employ slots/holes to mount rails only as needed. It is possible to mount weaponlights without having to purchase an aftermarket rail, saving you quite a chunk of change if that is the main reason you’re buying a handguard, but options are more limited.



    Magazines

    Saying magazines are important is a lot like saying water is wet. It’s obvious. However, the AR wasn’t designed to feed from curvy 30-round magazines, but from straight 20-round magazines. Fortunately, technology has progressed a bit and today we have a lot of choices for good, reliable magazines. Right now the best magazine available is the Magpul Pmag. It is probably the most durable and reliable AR-15 magazine money can buy, and certainly is the most durable and reliable mag at its price point ($10-15). Buy them, they will not disappoint. Other good choices include the Lancer L5 and TangoDown ARC. If plain ol’ USGI magazines are more your speed, Bravo Company sells Brownells and D&H Industries magazines with Magpul Enhanced Followers and your choice of chrome-silicon or stainless steel mag springs.



    Lights and Light Mounts

    For any gun meant for “social use”, consider a weaponlight to be mandatory. How often have we heard on the news someone getting shot late at night by their loved one after being mistaken for a burglar? For law enforcement, do you think there might be unarmed bystanders in a suspect’s home?

    There are too many good lights, and ways to mount them, to get into specifics on each. I will say that Surefire is one of, if not the, most popular manufacturer of weapon lights; other popular choices include Insight Technologies, Pentagon, and Streamlight. Where and how you mount a light will depend on how you plan to grip the weapon. Pressure pads can allow you to mount a light further away from your grip while still being accessible, but they’re costly. Ideas on how to mount weaponlights can be found here. Regardless, get a light and get training with it. Many well-known and reputable training outfits offer a low-light / no-light specific course (as with Surefire Institute) or include low-light / no-light components within their other courses.



    Muzzle Devices

    By and large, the USGI birdcage flash suppressor is sufficient for most purposes. It’s fairly small, durable, and typically comes with the barrel so it costs nothing. However, in terms of actual flash suppression, it has nothing on the AAC Blackout, Smith Enterprises Vortex, and Yankee Hill Phantom, ranked in order of most to least effective. These are outstanding at suppressing the flash of the 5.56 NATO, which might not be noticeable or sound important until you have the opportunity to shoot indoors and in low-/no-light. They are also conveniently long enough to bring your 14.5” barrel over the 16” mark when pinned.

    Compensators I’ll be leaving alone*, and indoor shooting is why. This is also why I’d ax the newer flash hider / compensator combos. On the other hand, “blast redirectors” (for lack of a better name for them) might be quite handy for shooting indoors. I call them “redirectors” because they direct all of the blast (light and sound) downrange instead of to the sides. There are only two biggies on the market: the DPMS Levang Linear Compensator and the Noveske KX3. This is probably the one time I will ever recommend something DPMS over something Noveske. By all indications, the Levang comp works just as well as the KX3, but is smaller, lighter, and a lot less expensive (as in, a quarter of the cost). The Levang requires a crush washer, the KX3 does not.

    *There is something of a caveat in the BattleComp. It is a compensator that more-or-less redirects the blast in a similar way to the Levang comp, mitigates flash almost as well as the standard A2 birdcage, and is the same size as said A2 flash hider. testimonial is very consistent among law enforcement users and it has earned extremely high praise. I have never used one myself, but I know better than to ignore folks smarter than me. By all indications, the BattleComp is a viable option as a muzzle device for a home defense rifle.

    The last type of useful muzzle device for the AR-15 is the most obvious, and probably the coolest: sound suppressors. They kill flash, significantly cut down the sound, are a lot larger, and cost worlds more. Good ones will run $800 and up, and virtually all suppressors are adding 16+ oz and 4-5” in overall length and to the rifle. Sound suppressors are definitely viable options for those in states where they are permitted, and for those willing to deal with paperwork and the tax stamp. A few dozen different makes and models can be found here. Tactical Operations reportedly makes some of the best suppressors you can buy, but Mike R. would prefer you called him to talk details (Awesome guy, be sure to have some spare time...).



    Slings

    As when I originally wrote this article some 3 years ago, I am still conflicted on the subject of slings. I am not convinced that in a home-defense scenario you will have time to "install yourself into one" as our own gasmitty describes. However, a strong argument can be made for slings when manipulating the rifle with one hand to grab family members (or suspects) with the other. To me, the sling seems more necessary on a patrol rifle than on a home-defense rifle.





    (Continue to Part 5)
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    Part 5 – Ancillary Stuff


    "Ancillary" in the context of this guide refers to those components for the AR-15 worth mentioning, but that do not directly influence the reliability of the weapon and can be upgraded to make the weapon work better for you. This is about ergonomics and how to make a rifle more effective for the person handling it. Many of the components are required on the gun for it to function (such as pistol grips and buttstocks), but all of them will add to, take away from, and otherwise change the weapon and how you use it.



    Pistol Grips

    For virtually everyone in the United States over the age of 5, the stock (A1 or A2) AR-15 pistol grip sucks. It’s too small, does not line your hand up naturally to interface with the trigger, and necessitates rubbing that irritating “gap” under the rear of the trigger guard. There are a lot of different grips out there that remedy this. Bravo Company sells a number of popular ones. These are all $20-$40 upgrades and are obviously very personal, but any that fits you will be an upgrade over the stock A1 or A2 pistol grips.



    Stocks

    Stocks... well, truthfully there are far too many stocks to “sum up”, but there are a few companies who should be looked at if you want to migrate away from the standard A1, A2, or CAR stocks. Magpul and VLTOR make outstanding buttstocks, and Troy Industries has recently jumped in with their Battle Ax CQB stock. The B5 Systems Enhanced SOPMOD and SOPMOD Bravo are also excellent choices. Like pistol grips, choosing a stock to upgrade to is personal. Be warned: if you choose a collapsible stock and have facial hair, expect it to be pulled. There is less available for fixed stocks, but Ace and Defensive Edge are thought highly of and are popular enough to find good reviews for.



    Vertical Grips et al.

    There are a lot of options for vertical grips, but they’re all designed for the same basic purpose: provide the user with better control over the weapon, more comfortably. The latter it does well – there’s not much more comfortable than the beer-can grip held out in front of you. The former, on the other hand, is questionable. Held in the beer-can style, it becomes more difficult to control the weapon along the barrel. Many users have taken to modifying their grip on the weapon such that the vertical grip is only a handstop or reference point, which led to the development of the stubby vert grips. Knight’s Armament took it a step further and developed a plain ol’ rail mounted handstop. After reevaluating how people are holding their rifles and why, Magpul also developed the Angled Forward Grip, or AFG. Whether and how one uses a forward-mounted grip, and which grip they use, is highly dependent on how the rifle is being shot.





    (Continue to Part 6)
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    Part 6 – Ammunition


    Ammunition for self-defense is very interesting subject. It is so interesting, in fact, that people will invest energy in arguing the merits of one caliber versus another with incredible regularity. Some are well-reasoned. Most are not. Instead of simply listing good ammunition for the AR-15, we’ll first look into some of the basic mechanics of how a bullet wounds, discuss and dispel a couple popular myths, and describe a brief history of the 5.56x45. Hopefully, by the time you get to the list of “good ammo” you’ll understand why it is good ammo. Bewarned: this will be a long post.

    While AR-15s can be had in a staggering number of calibers, virtually anything that can fit in the magazine, we’ll be focused exclusively on the 5.56x45 NATO. It is the most known caliber for the rifle, the best supported in terms of factory and reloading options, and has the greatest number of durable and reliable factory rifles available. It also simplifies this discussion immensely.




    How Bullets Work

    As I’m sure many of us know, the human body is a remarkably durable piece of equipment. It can withstand some pretty incredible traumas and still support itself well enough to fight and possibly survive. There are many stories about American GIs taking a burst of 8mm from a German MG 34 and surviving, and just as many describing German soldiers still fighting after taking half a clip of .30-06 from an American Garand. Yet, many people die every year from the diminutive .22 long rifle, and many more from small caliber pistol rounds like the .380 ACP and .38 Special. Heck, some people don’t even know they’ve actually been shot, and others drop even if they haven’t been shot!


    In Transit

    Let’s take a look at what bullets actually do, so we might understand the above examples and why they aren’t as complex as they might look.

    A bullet leaving the barrel of a rifle is given spin by the barrel’s rifling. A spinning bullet is a lot like a gyroscope, always trying to turn the same way. Spinning bullets, like spinning gyroscopes, are harder to deflect from their path than non-spinning bullets and give the bullet a much straighter flight path. However, a lot of forces are acting on the spinning bullet: gravity, air resistance, recoil, bullet motion, and even the spinning itself. These forces cause the axis around which the bullet rotates to not be perfectly aligned with its flight path, and the bullet to wobble slightly along the way. The net effect is a very mild corkscrew-like transit. The “wobble” creates what we call yaw, or the angle of the centerline of the bullet relative to its flight path. The variance yaw will change over the course of the bullet’s flight, being greater at close ranges before the bullet can stabilize, less after the bullet stabilizes (and “wobbles”/yaws less around its axis), and greater again as it slows down enough to lose stability and deviate from its flight path.

    Visual aid: spin a top on a table. At first, it wobbles a bit, and eventually stabilizes before it slows down and begins to wander more from its axis. The spinning bullet is doing exactly the same thing, only horizontally and at much greater speeds.


    Upon Arrival

    Now we know what the bullet does on the way, but what does it do once it “gets there”?

    First, Bullets damage in basically two ways, also paraphrased from Dr. Roberts. The first is crushing of the tissue the bullet physically comes in contact with, and the second is the stretching of the tissue adjacent to the bullet’s path. The localized crush creates a space where tissue is permanently destroyed. This space is the permanent wound cavity. Formation of the permanent cavity is consistent and reliable. The “temporary” cavity is a little more complicated. Tissue surrounding the main permanent cavity is briefly pushed aside, driven radially outward by the bullet’s passage. I say “briefly” because this empty space is only empty for a moment; the elastic recoil of the tissue will subside and move back toward the permanent cavity. This is the temporary wound cavity, and is a lot harder to predict. Because most things in the body have different degrees of elasticity, it’s hard to tell what will be damaged by the stretch and what won’t be. Still, the several inelastic tissues (liver, kidney, spleen, pancreas, brain, and completely fluid or gas-filled organs) are highly susceptible to damage from this temporary cavity.

    A bullet striking a person will first penetrate flesh and begin to slow down rapidly. Flesh is a lot stronger than most people realize, and will stretch significantly before it tears. It also rests on other elastic tissues, like muscle and almost everything else in the body. The sudden increase in drag on the bullet and rapid loss of velocity overcomes its rotational stability and may cause the bullet to yaw… only instead of the 0-4 degrees the bullet may yaw in flight, it may yaw more than 90 degrees. To quote Dr. Gary Roberts here:

    “If the bullet yaws, more surface area is in contact with tissue, so it crushes more tissue, creating a larger permanent cavity. When a bullet yaws, it also displaces more of the surrounding tissue, increasing the temporary cavity size. Both the largest permanent and temporary cavities are produced when the bullet is traveling sideways at 90 degrees of yaw, allowing the maximum lateral cross sectional area of the bullet to strike tissue and displace the greatest amount of tissue. Longer and wider bullets have a greater lateral cross sectional area and thus create a larger permanent cavity when they yaw.”

    For the readers wondering how bullet fragmentation plays into this, I’ll defer again to Dr. Roberts:

    “Projectile fragmentation in tissue can also greatly increase the permanent cavity size. When a rifle bullet fragments in tissue, each of the multiple fragments spreads out radially from the main wound track, cutting its own path through tissue. This fragmentation acts synergistically with the stretch of temporary cavitation. The multiply perforated tissue loses its elasticity and is unable to absorb stretching that would ordinarily be tolerated by intact tissue. The temporary cavitation displacement of tissue, which occurs following the passage of the projectile, stretches this weakened tissue and can grossly disrupt its integrity, tearing and detaching pieces of tissue.”

    In short: fragmentation tears into the elastic tissue while it's being stretched, making the permanent wound cavity bigger.


    Myths

    There are two particular myths that I’m going to address: so-called hydrostatic shock and “knockdown power”.

    Regarding hydrostatic shock: much of the support for the concept comes from the man promoting it drawing parallels between concussive blasts and the shock waves generated by a bullet impacting the limbs or torso. I have yet to see Dr. Michael Courtney, the most vocal proponent of hydrostratic shock, able to demonstrate a parallel between damage due to concussive blasts (read: bombs) and the shock wave generated by a bullets. Claims concerning neurological damage are especially questionable to me, as a college student studying the brain in particular. Incapacitating neurological damage (really any neurological damage…) due to the shockwave from a projectile impacting the limbs or torso is unheard of among both peers and professors. If hydrostatic shock existed I would expect to see more evidence in support of it given the frequently of gunshot wounds that occur in the United States and conflicts like those in Iraq and Afghanistan.

    Dispelling the myth of “knockdown power” is a lot more straightforward. As FBI Special Argent Urey Patrick describes on page 9 of this outstanding article (from which I borrow the title of the next section), a bullet simple does not generate the momentum necessary to knock someone down. This is demonstrated quite clearly using simple ballistic pendulums. Simple physics.



    The Human Target

    Now that we understand what a bullet does once it hits someone and how it wounds, let’s take a quick look at what we needs it to do to a human target.

    There are only two definitive methods of stopping someone with a bullet: hit their central nervous system or bleed them out. The first option produces more or less instantaneous results, while the latter can take a while. Obviously the former is more desirable than the latter; it doesn’t take a very long time or very much effort for someone, even mortally wounded, to pull a trigger. As Dr. Ken Newgard describes and Dr. Gary Roberts reports (also in the link provided above):

    “A 70 kg male has a cardiac output of around 5.5 liters per minute. His blood volume is about 4200 cc. Assuming that his cardiac output can double under stress, his aortic blood flow can reach 11 Liters per minute. If this male had his thoracic aorta totally severed, it would take him 4.6 seconds to lose 20% of his total blood volume. This is the minimum amount of time in which a person could lose 20% of his blood volume from one point of injury. A marginally trained person can fire at a rate of two shots per second. In 4.6 seconds there could easily be 9 shots of return fire before the assailant’s activity is neutralized. Note this analysis does not account for oxygen contained in the blood already perusing the brain that will keep the brain functioning for an even longer period of time.”

    In order for a bullet to get to the “good stuff” from any angle, it needs to be able to reliably penetrate at least 12-14” of tissue. Turn a person partially sideways, and assume one or both of their arms are outstretched toward you (as if, say, pointing a gun at you). Look at the material between you and their vitals: all of the muscle and bones in the hands, forearm, elbow, upper arm, shoulder, and the chest. Now add clothes. Even a skinny junkie or malnourished third-world insurgent will have quite a lot of “stuff” in the way of their vitals. Start stacking on muscle and it gets even worse.

    As a bullet penetrates tissue and before it yaws, it leaves a narrow wound channel referred to as the “neck”. The “neck” of a wound profile is the skinny channel before the bullet fully or partially upsets to create a larger cavity. Typically, a short (less than 4”) neck is better, as it indicates early upset after penetration; in fact, our ideal wound profile will have a short neck followed by rapid expansion, a large permanent wound cavity, and reliable penetration. Remember how we want at least 12” of penetration, though? Though it may be hard to visualize, many types of ammunition in several calibers, including the 5.56, can exhibit early this upset while also providing the depth of penetration we want. The largest wound cavity will not likely extend as far back as 12”, parts of the projectile will certainly penetrate that far.






    Psychology

    Psychology can, and frequently does, play a role in stopping a threat, but it’s not reliable. A threat can be incapacitated psychologically but not physiologically. The same man who would collapse for fear of his assumed injuries while sober might not even notice them when doped up, drunk, or high. That is to say, psychology can actually prevent incapacitation as well as initiate it. If we’re pulling the trigger, we want the threat stopped right damn now, or as close to right damn now as is possible. Relying on the psychological effects of being shot to end a threat is simply not viable.



    The 5.56x45 NATO

    By now you have a good understanding of how a bullet flies, how it hurts, and what we need it to do. Now we can look at the 5.56x45 NATO and perhaps put to rest some of the misconceptions about the round.


    History

    Immediately after the Korean conflict ended, the small-arms community buzzed at the prospect of replacing the M1 Garand and M1 Carbine. Additionally, several important events occurred that would eventually lead to the creation and adoption of the 5.56x45 NATO.

    To kick it off, Britain’s Dr. Richard Beeching conducted tests similar to the United States’ 1920s pig tests and came to the same conclusion: most infantry engagements took place within 600 yards and full-power rifle rounds (our .30-06 and their .303 British) were just too powerful at those ranges. They more often went through their targets and did not injure them as well as a smaller 6.5-7mm caliber would. In 1952, Norman Hitchman’s “controlled salvos” concept evolved into Project SALVO, which suggested that a burst or volley of small-caliber projectiles can be effective at closer ranges while providing greater controllability in automatic fire. Following this, reports investigating both the potential of high-velocity .22 caliber cartridges and how infantrymen actually fight were released. Special attention was paid to the ranges at which infantry fight, especially to the poor accuracy of infantrymen at extended ranges. Except for penetration of barriers, small caliber, high velocity (SCHV) cartridges appeared superior to U.S. military .30 caliber cartridges at the ranges relevant to infantry combat. Later tests in Vietnam circa 1962 confirmed Hitchman’s previous notions about SCHV cartridges. The Marine Corp Landing force development center evaluation of the AR-15 in 1963 concluded that between the M14 and AR-15, the AR-15 would be the more effective combat rifle for the USMC; only the lack of a .223 machine gun prevented them from recommending adoption at the time.

    Despite heavy institutional resistance, skullduggery, and mismanagement (mostly from the Army), the AR-15 is eventually adopted by the United States military. Whatever some may think, the 5.56x45 NATO was not selected because of its reduced terminal effectiveness (“Hurt one so he must be carried out…”) or because maximum firepower (read: most ammo) trumped all else. The SCHV concept has been repeatedly proven to be a sound one, even limited to silly Hague-compliant, non-expanding ammunition. The single biggest criticism of SCHV rounds is their poor barrier penetration, which is a valid point of concern

    But it’s also pretty convenient. We civilians aren’t bound by Hague-convention nonsense, nor do we want a lot of barrier penetration. Cool huh?


    Wound Characteristics of SCHV Cartridges

    As noted by Dr. Martin Fackler, Dr. Gary Roberts, and others, wounding characteristics for small caliber, high velocity cartridges are someone unique. Specifically, they are more sensitive than other calibers to variations in angle of attack (AOA) and fleet yaw, bullet construction, and the target itself. This sensitivity is such that multiple people can give conflict reports on performance that are all accurate. The combination of high speed and small mass means that there is more inherent variability in performance in SCHV cartridges than there will be in larger or slower cartridges.

    Remember how bullets wobble while in flight, producing varying degrees of yaw? This helps determine what’s called “angle of attack”. Angle of attack (AOA) is simply the angle at which the bullet strikes a target relative to its flight path, or the degree of yaw as it hits something. As mentioned previously, the largest variation in yaw is at close-quarter battle distances: basically 100 yards and in for the M855. Doctor Gary Roberts describes the effects of AOA variances on page 8 of his 2008 NDIA presentation. At a higher AOA, say 2-3 degrees, even FMJs provide acceptable terminal ballistics. But at 0-1 degrees, the exact same bullet will frequently pass right through the target. Where some soldiers are describing great success with the M855 and others are describing serious deficiencies, both are correct and are telling the truth. SCHV cartridges like the 5.56x45 are very sensitive to AOA differences. Open-tip match bullets are much less susceptible to AOA variances, as are some of the better bullets that will be described below.


    (Images courtesy of Dr. Gary Roberts in his 2008 NDIA presentation "Time for a Change", pg8.)

    Fleet yaw is another issue worth mentioning. To quote Dr. Roberts, “Fleet Yaw is the terminal performance variation caused by inherent variability in each rifle and occurs in all calibers. 5.56 mm FMJ appears to suffer more Fleet Yaw induced variability than other projectile calibers & types.” As with AOA, open-tip match and other well-made bullets are less susceptible to variances by fleet yaw. Other calibers are less sensitive to it as well.

    Bullet construction and target material will sound similar to the above: SCHV cartridges are generally pickier about what they go through and how well they go through it than are larger calibers. For example:



    The Barnes 70 gr TSX is an excellent bullet, but against auto glass the jacket petals sheer off and the bullet behaves something like a wadcutter. You’ll get penetration, but better choices can be had. While clothing seems to play a large role in the effectiveness of handgun rounds, it does not seem to be as important for rifle rounds. I am seeking clarification of this.



    The List

    Alright, alright, enough delay. What rounds are good choices for 5.56x45?

    “Zhukov” at AR15.com put a lot of time and energy into compiling one hell of a defensive ammo resource here. Since it deserves recognition, and is the first time I get to be brief in this entire section, I present to you a nice, easy-to-read, too-long-in-coming list of good self/home-defense 5.56 ammo:

    “If Barrier penetration is NOT an important factor AND your rifle can stabilize them (1:9 minimum twist rate):

    * Hornady 75gr OTM loads
    * Nosler 77gr OTM loads
    * Sierra 77gr SMK loads


    If Barrier penetration is NOT an important factor AND your rifle can't stabilize the heavy 70+ grain bullets:

    * Sierra 69 gr SMK loads
    * Hornady 68 gr OTM loads
    * Winchester 64 gr JSP (RA223R2)
    * Federal 64 gr TRU (223L)
    * Hornady 60 gr JSP
    If Barrier penetration IS an important factor
    * 62 gr Federal bonded JSP Tactical (LE223T3)
    * 55 gr Federal bonded JSP load (Tactical––LE223T1 or identical Premium Rifle––P223T2)
    * Swift 75 gr Scirocco
    * 60 gr Nosler Partition JSP
    * Barnes all copper TSX/TAC-X (inferior performance through glass compared to a TBBC)


    If using a short-barreled weapon AND your rifle can stabilize them (1:9 minimum stwist rate):

    * 70 gr Barnes TSX/TAC-X
    * 75 gr Swift Scirroco
    * 75 gr Hornady OTM
    * 77 gr Nosler OTM
    * 77 gr Sierra SMK


    If using a short-barreled weapon AND your rifle can't stabilize the heavy 70+ grain bullets:

    * 62 gr Federal bonded JSP Tactical (LE223T3)
    * 55 gr Federal bonded JSP load (LE223T1 or P223T2)
    * 60 gr Nosler Partition JSP
    * Barnes 55 gr TSX/TAC-X”

    *A note on bullet-size for fragmenting and non-fragmenting bullets from Dr. Roberts:

    “Keep in mind, that with non-fragmenting bullet designs, heavier bullet weights are not necessarily better, especially at closer ranges and from shorter barrels. As long as penetration and upset remain adequate, it is possible to use lighter weight non-fragmenting bullets and still have outstanding terminal performance. With fragmenting designs, a heavier bullet is ideal, as it provides more potential fragments and still allows the central core to have enough mass for adequate penetration.”





    (Continue to Part 7)
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  9. #8
    VIP Member Array BAC's Avatar
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    Part 7 – Maintenance


    So who here knows how to take care of their AR-15? Are you sure? Do you know what constitutes “maintenance” of the AR-15, or how much cleaning is actually needed? Would you believe me if I said the vast majority of shooters don’t?

    Contrary to popular belief, the AR-15 is not a fragile weapon dependent on meticulous cleaning. It is at least as reliable and robust as the M14, to which it is so often compared, as cited by the Infantry Board in 1958, the CDEC in 1959, Aberdeen Development and Proof Services in 1960, and USMC in 1962. Over 40 years later, trainers like Pat Rogers and Mike Pannone continue to demonstrate their ARs going thousands of rounds between malfunctions, with and without cleaning and preventative maintenance.

    What kinds of round counts am I talking about? Jeff, a long time police officer and SWAT officer from Colorado at 03 Design Group, had this to say in a January 2010 article:



    “On 12-24-09 I contacted Pat Rogers to see what the current round count of the BCM 16" Mid-Length that he has been loaning out to students. Pat refers to this BCM Mid-Length as "Filthy 14" and provided me with the following information on this gun:

    Filthy #14 is the most used, and has (as 12-24-09) 28905 rounds down range. The barrel is original. It has never had a brush put through it.

    -At 16,400 rounds bolt lug cracked. Replaced the bolt carrier group

    -At approximately 26,000 rounds fired a 5 shot 50m group that went into 0.5". This might not be that tight at 100 meters.

    -At 26,450 rds had 3 failures to extract. Replaced BCG and cleaned gun for the first time

    We use only SLip2000 EWL for lube and Slip 2000 725 to clean.

    **All of the rounds were fired during class (at the rate of approximately 1,250 rounds every 3 days)**

    I do not recommend allowing the gun to go this long without PM (preventive maintenance). However, we wanted to see how far we could take this particular gun (#14) without being burdened by the myth of meticulous cleaning.
    Keep in mind the punishment that Pat Rogers' BCM mid-length has been put through. The gun is being shot approximately 8 hours a day in a tactical training class environment at the rate of approximately 1,250 rounds every 3 days. Very few people have the time, money, or effort to run a gun like that for 28,905 rounds. This upper has the standard barrel, not the new BFH (cold hammer forged) barrel.”




    Yes, that’s 29,000 rounds out of a 16”-barreled, midlength AR-15. While a little less dramatic than Filthy 14, Mike Pannone described firing 15,000 rounds from his Noveske N4 carbine and experiencing 6 malfunctions and 3 failures to fire. In his words, "All were attributable directly to bad magazines or bad ammunition." Unlike Rogers, Pannone cleaned the rifle every 1000 to almost 4000 rounds, replaced the gas rings at 8660 rounds as preventative maintenance, and used Sprinco Machine Gunner's Lube. Heck, even the NY Times (unwittingly or intentionally) demonstrated pretty damn impressive performance from an M4 and M4A1. These reports are coming from men who see hundreds of thousands of rounds downrange per year, one of whom literally wrote the book on how to properly take care of an AR. Hearsay this is not.

    Hopefully I’ve caught the interest of those who didn’t believe the AR-15 capable of such endurance. Now we’ll be a brief look at what needs to be looked at on the weapon, and how to clean it.



    Cleaning

    Most people will eventually succumb to the urge to clean the crap out of their weapon. On the “how-to” of rifle cleaning, I’ll defer to Chad (“borebrush” if you frequent Lightfighter), probably one of the best armorers to ever have the title; he knows a couple things about the M16 family of weapons. He is also a Marine, which means I can’t quote him word for word on this site, but I can come pretty close:

    Pull the carrier. Squirt some Carbon Killer on the bolt face, and knock the <crap> off of the face.

    Squirt some Carbon Killer in the chamber, turn a chamber brush a few times.

    take a 20oz water bottle, pour it down the bore from the chamber. Let it drain. Pull a boresnake a few times.

    Wipe off the Carbon Killer residue with a rag. Apply EWL to the bolt, reass the BCG.

    visually inspect the trigger group. function check it for any breakages. If its truly <dirty>, blast out the lower with some more Carbon killer. Dump that <crap> out. Use some Dust off (hold it upright) and blow out the rest of the <crud>. Blast some EWL into the lower on the wear points.

    Reass the gun. FINE. Took longer to type this <crap>.
    As for cleaning the bolt:

    Remove the extractor and clean the extractor recess. I do this after I've suspended the bolt in a jar of Slip Carbon Killer for 10 or 15 minutes. Means little scrubbing. While the bolt is soaking I clean the interior of the upper/chamber with Carbon Killer, chamber brush if needed, and Qtips/Rags. Change patches, QTips, and Rags as often as they get dirty. You don't wipe your <butt> with the same <crap> ticket over and over do you?

    I do not waste time on the tail of the bolt, if it doesn't wipe off, it stays. Don't pick at the gas rings. Just wipe any <crud> off of them so that you can insure that they aren't missing or broken and bent.

    I do get that firing pin channel clean by pipe cleaner and Slip, then blast it out with air.

    While I'm cleaning that bolt I soak the carrier in the Carbon Killer. Blast it out with air, then lightly brush and wipe the thing down. Same goes for the firing pin, extractor and cam pin. Be sure to get the Cam Pin raceway clean, as carbon there can cause drag. Again, carbon there wont shut a gun down as long as it's lubed.

    Once you are done with the bolt and carrier, reassemble it. ( don't leave the parts sitting around so that you can lose them.) Check your gas rings by setting the bolt carrier vertically on the bolt face. It should not fall closed under its own weight. If it doesn't, then bump the table, it should fall part way but not completely foreward. If it does, you need new gas rings.
    The bore is fairly easy… if you decide to clean it. Pat Rogers and a host of other high-volume shooters rarely, if ever, clean the bores of their rifles. However, should you feel the need to, Chad suggests running a wet patch of solvent through the bore and letting it sit while you clean the rifle. As he says, “the application of uncommon sense”. Also, while you’re running patches through the bore:

    DO NOT HARPOON THE CHAMBER WITH YOUR BOREBRUSH or EYELET. It is not designed to work that way. You feed the rod from the chamber end, while pulling the brush/patch through the bore. When done this way it is a one person job. If you harpoon it, you will bend <things>, break the rod, or get the whole thing stuck as the brush bends, or your patch wraps the eyelet and causes a restriction. Pull the brush a couple passes, then go to the patches. Use a patch only once. Again, <crap> tickets and your <butt>.
    There. You’re done. Pretty easy, huh?

    Excessive cleaning, by which I mean scrapping, scratching, etc., will do a lot more harm than good. A lot of folks complain about baked on carbon, but if you’re running the rifle wet like you’re supposed to it shouldn’t be that bad. “I wonder why my eggs keep sticking and burning to this hot dry skillet?” (Another nugget from Borebrush)



    Maintenance

    While you’re cleaning the rifle, you should also be doing preventative maintenance. This means checking the wear for wear parts, the checking for wear on non-wear parts, and generally looking for things that could go wrong before they actually go wrong. Shiny places are fine, but deeper wear is not. Look for fractures, cracks, burs, and similar problems.

    As you visually inspect the weapon, look for symmetry.

    -Do the hammer spring legs on either side of the hammer and trigger, mirror each other? Does the hammer swing true? Or is it canted or not parallel in the receiver?

    -Is the gas tube parallel with the charging handle raceway?

    -Does the carrier slide forward easily without any noticeable wiggle of the gas tube (without bolt installed of course).

    -Is there only one lug on one side of the extractor?

    -Does the Firing Pin Retaining Pin look like hammered ****?

    -Are my sights canted?
    Keep in mind, that like all mechanical devices there are certain items that will wear out. You will eventually need to replace the gas rings on the bolt (the procedure for determining so described above). After 5k rounds, you’ll eventually need to replace the bolt itself. The action spring will eventually compress too much (10 1/16" to 11 1/4" for carbines, 11 3/4" to 13 1/2" for rifles), and that’ll need to be replaced too. The barrel should last you many, many thousands of rounds, especially if yours is one of the barrels I mentioned earlier. When the throat finally does wear enough to consider the barrel shot-out, it’s probably about time to retire that upper.

    The lower receiver assembly, barring the action spring, really shouldn’t see anything worn out. Chad/Borebrush notes that the basic fire control group in an AR-15 eats up hammer trigger pins and disconnects. Whether that means a lot to us as civilians as opposed to he as a military armorer is for you to decide. His suggestion is the Geissele SSA trigger pack. The other option is to just consider hammer trigger pins and disconnects to be wear items that will eventually need replacing. Completely your call, depending on what you want out of the rifle.



    “Keep It Running”

    Mr. Pat Rogers wrote an article in SWAT magazine in 2006. In it he also dispels certain myths about cleaning, as well as describes how to keep the rifle running while it’s actually being run. I strongly suggesting reading this article, which can be found online as a pdf here. Short version: run it wet, check parts for wear, run it wet, replace as preventative maintenance dictates, and run the damn rifle wet. Slip 2000 EWL, Sprinco Machine Gunner’s Lube, WD-40, Mobile 1, etc. Whatever you find that works, use. Just don’t run the rifle dry and expect stellar results.



    You are now armed with knowledge of how to take care of your rifle. Go forth and shoot the heck out of it.
    jonconsiglio likes this.
    RIP, Jeff Dorr: 1964 - July 17, 2009. You will be missed.


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  10. #9
    VIP Member Array BAC's Avatar
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    References

    Under construction. This one will be a bit slower now that the rest (more important stuff) is done.
    Pete63 likes this.
    RIP, Jeff Dorr: 1964 - July 17, 2009. You will be missed.


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  11. #10
    VIP Member Array BAC's Avatar
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    Spare. Just in case.
    RIP, Jeff Dorr: 1964 - July 17, 2009. You will be missed.


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  12. #11
    VIP Member Array BAC's Avatar
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    Heh. It seems that in making the topic a sticky I can no longer edit any of its pages. I'll have to work on that.
    RIP, Jeff Dorr: 1964 - July 17, 2009. You will be missed.


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  13. #12
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    Quote Originally Posted by BAC View Post
    Heh. It seems that in making the topic a sticky I can no longer edit any of its pages. I'll have to work on that.
    About the best I can offer at the moment is to let me know when you have some stuff you want to work on and I'll unsticky then re sticky.

    I'm going to be away from my 'puter for a few hours, I assume you want to work on it now. So I'll unstick for now; but be aware that once it gets a certain time, you cannot edit it anyway. I'm not sure what that limit is.
    "Just blame Sixto"

  14. #13
    VIP Member Array BAC's Avatar
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    That's one idea, yeah. I'll ask Bumper if there's a lower maintenance way of doing this. I'm guessing vBulletin doesn't have very high-tech permissions.

    Edit: interesting on the limit for editing. Do you know if editing it in the meanwhile resets the timer?

    Edit 2: Evidently, even unstickied the posts can't be edited. Hm...
    RIP, Jeff Dorr: 1964 - July 17, 2009. You will be missed.


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  15. #14
    Member Array Drgnfly's Avatar
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    Nicely done sir.

  16. #15
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    Well, I'll restickie then. I'm not much help with the technical stuff of the forum- but Bumper no longer owns the forum and isn't around much.
    "Just blame Sixto"

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