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Lowest price? I think the CMMG piston gun can be had for around $900. I have never heard anything bad about them, but I don't own one.
 

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Lowest price? I think the CMMG piston gun can be had for around $900. I have never heard anything bad about them, but I don't own one.
I don't need the lowest price. It's more about if anyone on this site has one and would like to share their opinions on having this type of AR.
 

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If you absolutely have to have a piston driven gun I would suggest the Sig 5.56. Which was purpose build for the task, and it takes standard AR mags.

From my reasearch, every piston driven AR eventually develops carrier tilt wear. If you are using this for range time and sporting events, then that isn't a biggie. But if it is your SHTF rifle that can become a major issue.
 

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Does anyone have one and if so which brand and do you think it's worth the extra money?
I don't have one, but I also don't think it's worth the extra money. The only real advantage a piston-driven AR offers over a properly built, well-lubed "normal" AR is if you like shooting with suppressors.


-B
 
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If you absolutely have to have a piston driven gun I would suggest the Sig 5.56. Which was purpose build for the task, and it takes standard AR mags.

From my reasearch, every piston driven AR eventually develops carrier tilt wear. If you are using this for range time and sporting events, then that isn't a biggie. But if it is your SHTF rifle that can become a major issue.
Carrer tilt wear? WTH? After how many rounds? I am getting a Ruger SR-556 and I have never heard of this stuff you call tilt wear. :tumbleweed:

Explain please................
 

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I found this(The first reason is carrier tilt. The piston places torque on the gas key causing the back of the carrier to tilt down causing scrapes along the buffer tube and shearing gas keys. The AR platform was designed as a free floating bolt carrier. Now some companies have been able to remedy this such as LWRC by installing carrier guide rails and going to solid one piece carriers. However, I still think that the AR was designed as a gas operated gun and I see many operating just fine. I have seen just as many problems with piston guns. I can understand the cleaner arguement as the DI system can be very dirty, especially with suppressed applications. However, I am very particular about cleaning my rifles. Anyways, I am no expert nor claim to be one just giving my view about the other side of pistons on the AR-15 )
 

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Here is an interesting brief discussion about the DGI (direct gas impingement) vs piston-rod operating systems: click.

Are the FN SCAR Weapons (MK16 and MK17) Necessary? And do we really need to replace the Colt M4/M4A1 Carbine?

By David Crane
defrev (at) gmail (dot) com

May 20, 2009

According to Army Times magazine, The 75th Ranger Regiment is scheduled to battle test the Special Operations Combat Assault Rifle (SCAR) very soon. The Rangers will reportedly be taking 600 FN SCAR rifle/carbine/subcarbine/SBR (Short-Barreled Rifle) weapons packages into battle, but DefenseReview doesn’t know how many of these are the 5.56×45mm NATO (5.56mm NATO) FN MK16 (formerly SCAR-Light a.k.a. SCAR-L) assault rifle/carbine/subcarbine/SBR variant, and how many are the 7.62×51mm NATO (7.62mm NATO) FN MK17 (formerly SCAR-Heavy a.k.a. SCAR-H) battle rifle/carbine/subcarbine/SBR variant.

The SCAR weapons are select-fire and operate via a short-stroke gas piston/op-rod (operating rod) (SSGP/OR) mechanism vs. the Colt M4A1 Carbine’s direct-gas-impingement (DGI) a.k.a. direct-impingement gas (DI gas) operating mechanism and were designed and developed to replace the Colt MK18 CQBR (Close Quarters Battle Receiver) 5.56mm SBR, Knight’s Armament (KAC) MK11/SR-25 7.62mm semi-auto sniper rifle, 5.56mm MK12 SPR (Special Purpose Rifle) (5.56mm), and the M14 7.62mm battle rifle. The SCAR weapons are modular, and military operators can choose barrel lengths of approx. 10″, 14″, and 18″ for the MK 16 and approx. 13″, 16″, and 20″ for the MK 17. The MK16 takes a 30-round magazine, and the MK17 takes a 20-round mag. The SCAR weapons offer a reported 80% parts commonality between the two variants.

Defense Review recently spoke to one of our professional contacts in the tactical firearms community, and he told us on the phone that the MK16/SCAR-L is for all practical purposes “dead”, meaning that it’s not likely to survive for very long, and thatthe SCAR weapons are continuing to experience teething problems in the field, i.e. breaking down. We don’t have confirmation/verification on this yet, so it’s just a rumor at this point. Anything’s possible, but we’ve spoken with people in the U.S.military Special Operations community who prefer either the AR-config HK416 (also written HK 416) for a gas piston/op-rod carbine/SBR solution or a good old-fashioned DGI Colt SOPMOD M4A1 Carbine or MK18 CQBR SBR for a DGI solution.

On the subject of piston-driven vs. direct-gas-driven weapons, while gas piston-driven weapons have been all the rage over the last few years, there’s a growing list of tactical AR cognoscenti, aficionados, and builders that are pushing back againt the march to gas piston/op-rod Nervana, making the case that piston-driven systems may not necessarily be a better mousetrap after all, and in a number of ways, are actually inferior to the combat-proven DGI operating system.

Direct-gas-impingement operation offers significant accuracy and weight advantages over gas piston/op-rod operation in AR (AR-15)-config weapons. For example, Heckler & Koch (HK) had to significantly thicken the barrel on the HK416 (also written HK-416) to counteract barrel flex caused by the forces exerted by the offset, reciprocating gas piston and operating rod. This barrel flex resulted in accuracy problems and vertical stringing of shots during full-auto fire. Understand that a gas piston/op-rod setup is already inherently heavier than a direct-gas-impingement setup, and thickening the barrel made the HK 416 heavier than it initially was.

It should perhaps be noted that a primary reason for the movement towards short-stroke gas piston/op-rod operation (and the use of the HK416 SBR, specifically) instead of direct-gas-impingement operation by elements in U.S. Army Special Forces and U.S. military Special Operations Forces (SOF) out of USSOCOM a.k.a. SOCOM was due to their desire to suppress 10.5-inch (10.5″)-barreled SBRs. Attaching a silencer/sound suppressor a.k.a. “muzzle can” to carbine or SBR changes the pressure and fouling dynamics of the weapon, and can cause reliability problems unless the weapon is specifically set up for suppressed use.

Even without a can attached, at 10.5″ inches, a DGI-operated AR15-config weapon like the Colt MK18 (formerly known as the Colt M4A1 CQBR)–which actually utilizes a 10.3″ barrel–is a bit too close to to the precipice of not working reliably, since the direct-gas operating system relies on a certain amount of barrel length to creat the correct amount of gas pressure for the correct amount of time, as well as a consistent level of gas pressure over time, to cycle the action (i.e. the bolt carrier group) and feed the next round. This “timing” element is crucial in a DGI AR-15 SBR for combat reliability. A suppressor just adds to the inherent and somewhat precarious pressure curve/timing issues of an AR-15 SBR.

However, if you add a high-tech self-lubricitous / self-lubricating, anti-rust/corrosion internal coating and a Precision Reflex (PRI) M84 Gas Buster Charging Handle - Military Big Latch, to a direct-gas AR, it may be possible to at least address the fouling issue. With this type of coating, DGI weapons may be able to handle the suppressed role (silencer/sound suppressor a.k.a. “muzzle can” attached to the weapon) just as effectively as a piston gun (unconfirmed/unverified). DefenseReview would have to test this, theory, however, and we may do this soon. The PRI M84 Gas Buster Charging Handle attenuates/mitigates hot gas and particulate matter backblast into the shooters face, which has been a criticism of suppressed DGI AR carbines and SBRs, including the M4A1 Carbine.

High-tech firearm coating technologies such as the Next Generation Arms (NGA) internal ceramic coating, the FailZero “AR-15 Basic Kit” and “AR-15 Extreme Duty Kit” nickel-boron (Ni-B)-coated AR-15 parts and components, and the Robar NP3 PTFE (polytetrafluoroethylene) a.k.a. Teflon)/electroless nickel coating/finish may reduce/mitigate internal “crud” a.k.a. fouling build-up inside a suppressed DGI AR-15 carbine SBR enough to allow it to work reliably at a high-enough round count to negate the gas piston/op-rod system’s advantages in this specific area. We’ll see.

It’s noteworthy that tactical instructor, author, and DefenseReview contributor Mike Pannone, a retired U.S. Army Special Forces (SF) operator, prefers a 12.5-inch (12.5″) barrel for a direct-gas-impingement AR-15 SBR. Since a 12.5″ AR SBR can utilize a standard carbine-length gas system (DGI), Pannone believes that 12.5 inches is the optimum barrel length for a DGI AR SBR, since it provides for optimum weapon utility. Basically, a 12.5″ AR-15 SBR offers the perfect balance of weapon compactness and versatility, reliability (provided by adequate barrel length to achieve the right pressure curve and timing), and muzzle velocity for adequate terminal ballistics/lethality. The one caveat is that the weapon has to be set up right, or “sprung right”.

In order to ensure this, Pannone developed the BHI Enhanced M4 SOPMOD Bolt Upgrade Kit being sold by Blackheart International (BHI), which, according to him, will solve the majority of M4/M4A1 Carbine and semi-auto-only AR-15 carbine reliability problems, all by itself. The kit includes a mil-spec extractor with a 5-coil extra-power extractor spring, Crane O-ring to elimate extractor bounce, 3 mil-spec gas rings, a mil-spec Black Buffer (H2 buffer), which also reduces exractor bounce, a Sprinco Extreme Duty Buffer Spring/Main Spring, which lasts 4-5 times longer than a standard buffer spring and “adds additional tension to absorb recoil; energy, and ensure reliable feeding, chambering and locking”, and a DPMS Rate Reducing Buffer. BHI says the following about the DPMS Rate-Reducing Buffer: “This buffer, along with the upgraded buffer spring will absorb more energy as the bolt cycles to the rear, slowing the bolt velocity and giving the shooter a much more manageable recoil impulse, and a decreased rate of fire on full-auto carbines. The heavier buffer will also ensure that feeding chambering, and locking on even a dry dirty chamber is positive and reliable.”

Provided the M4A1 Carbine (or semi-auto-only AR-15 carbine) is properly maintained by the end user and “sprung correctly”, i.e. outfitted with a BHI Enhanced M4 SOPMOD Bolt Upgrade Kit, Pannone argues that you’d be hard pressed to find anything better (i.e. more reliable), or even as good as the combat tested-and-proven Colt M4A1 Carbine.

It should perhaps also be noted that high-end tactical AR (tactical AR-15 weapons platform) builders John Noveske of Noveske Rifleworks, LLC and Nathan Roads of Next Generation Arms (NGA) both prefer direct-gas-impingement AR-15s to gas piston/op-rod ARs. DefenseReview found out about Noveske’s preference for DGI ARs during one of our interview sessions with him. Noveske and Roads also like the 12.5″ barrel length for DGI AR-15 SBRs.

So, does SOCOM really need the FN SCAR MK16 and MK17 weapons? Probably not. The fact is, while the SCAR family might potentially provide modularity and production cost advantages over the long term if SCAR is eventually adopted and it replaced all the weapons listed above that it’s intended to replace, it doesn’t offer any lethality advantages whatsoever over any of the already-fielded, combat tested and provenweapons it was designed and developed to replace.

The SCAR weapons simply aren’t revolutionary in any way with regard to combat capability and effectiveness. If anything, they’re more of an interim-level/bridging-the-gap solution until somone develops a truly revolutionary replacement for our currently-fielded weapons. Fact is, the MK-16/SCAR-L is a much more expensive proposition in the short term than just properly maintaining the legacy M4/M4A1 Carbines that are already in the system. Fact is, many SOCOM operators already prefer the HK416 (5.56mm) and HK417 (7.62mm) carbines and SBRs over SCAR for a short-stroke gas piston/op-rod weapon solution, if they’re going to replace the combat-proven M4A1 with anything. Fact is, the financial health of the U.S. military procurement system isn’t what it once was, due in large part to the financial realities of the country in general. And, fact is, there’s a new sheriff in town (Obama), and Demcocrat administrations aren’t traditionally conducive to a high level of military funding and support, at least not in the modern era.

And, again, rumor has it that SCAR weapons are breaking in the field (unconfirmed/unverified). Oh, and speaking of breaking, The HK-416 has apparently been experiencing its own share of parts breakages and reliability issues in the field, as well. Defense Review will further investigate the specific problems we’ve heard about for SCAR and the HK 416 as soon as we can.

Bottom line is that as time goes on, SCAR is looking more and more like an unnecessary indulgence and a waste of increasingly-scarce taxpayer dollars.

Editor’s Note: Mike Pannone (a.k.a. Michael Pannone) is the author of the M16/M4 Handbook and HK416 Handbook (also written HK-416 Handbook), which are invaluable resources to anyone who owns and/or uses an M4/M4A1 Carbine, tactical AR-15 carbine, or HK416 respectively. They’re also worthy additions to any tactical firearms library, even if you don’t own or use any of those weapons.

Company Contact Info:

FN Herstal USA (FNH USA) Military Operations
PO Box 896
McLean, VA 22101
Phone: 703-288-3500
Fax: 703-288-4505
E-Mail: [email protected]
Website: FNH USA

FNH USA Military Training Operations
Phone: 1-540-752-6200
Fax: 1-540-752-0967
 

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That was a great read ccw9mm! Thanks for posting that article!
 

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Here is an interesting brief discussion about the DGI (direct gas impingement) vs piston-rod operating systems: click.
Thanks that was pretty much was my understanding. Until this last year. According to Bushmaster rep I talked to they would not produce, piston driven upgrades or rifles until those problems carrier tilt accuracy were addressed and resolved. My guess is most of the reputable manufactures are finding ways to resolve the problems with piston driven rifles. Time will tell.

For now I have not upgraded my Bushy, clean with Gunzilla and she runs like a top. As BAC mentioned on another thread a FailZero bolt carrier may be a better investment.

Than again I am looking at a POF .308 at about the OP's price point. So far I can not find a bad review of the rifle. I think it is a better buy than the LWRC 308 I was looking at. Still trying to confirm if the POF is really a 308 or just a 7.62
 

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Than again I am looking at a POF .308 at about the OP's price point. So far I can not find a bad review of the rifle. I think it is a better buy than the LWRC 308 I was looking at. Still trying to confirm if the POF is really a 308 or just a 7.62
There is, for all practical purposes, no difference between .308 win and 7.62 NATO. I wish I had the link - but google is your friend if you don't want to take my word for it. But there is a good article where they analyze the difference in cartridge specifications - which do exist but they are slight. But more importantly no one has ever found a rifle stamped for either caliber that won't fire ammunition built to both specs.
 

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There is, for all practical purposes, no difference between .308 win and 7.62 NATO. I wish I had the link - but google is your friend if you don't want to take my word for it. But there is a good article where they analyze the difference in cartridge specifications - which do exist but they are slight. But more importantly no one has ever found a rifle stamped for either caliber that won't fire ammunition built to both specs.
The 7.62mm NATO cartridge has a maximum chamber pressure of approximately 50,000 psi, in the SAAMI book the .308 Winchester has a MAP (maximum average product) pressure of approximately 62,000 psi. Not all .308 will develop such pressures, but that they would be within manufacturing tolerances if they did so. My understanding is firing .308 Winchester ammunition in a firearm specifically chambered for the 7.62mm NATO risks damage to the firearm and injury to the shooter.

From GunZone
Chamber Headspace Gauges
.308 Winchester
GO: 1.630"
NOGO: 1.634"
FIELD REJECT: 1.638"

7.62 x 51mm NATO
GO: 1.635"
FIELD REJECT: 1.6455"

Chamber Pressures
.308 Winchester
MAP: 62,000 psi
MPSM: 66,000 psi
Minimum Proof Pressure: 83,000 psi
Maximum Proof Pressure: 89,000 psi

7.62 x 51mm NATO
Maximum: 50,000 psi
Proof pressure: 67,500 psi

Sources: .308 Winchester data from ANSI/SAAMI document Z299.4-1992, Pressure and Velocity, Centerfire Rifle Sporting Ammunition

7.62 x 51mm NATO headspace data from Jerry Kuhnhausen's M1/M1A shop manual.

Pressure data from TM 43-001-27: Army Ammunition Data Sheets Small Caliber Ammunition
I have not found one credible source of information on or off of the internet that says it is advisable to shoot 308 out a a 7.62 chambered weapon.
 

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Thank you LongRider. That is some very pertinent information.

side note ~ my SR-556 will be here on the 2nd. ;0
 

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If you want a reliable Piston Driven Rifle with a ton of Rail space I'd have to recommend a Masterpiece Arms MPAR 556. They are great guns and remind me of several different fire-arms I have seen over the years. Sort of like a FNC meets Ar-18. Rugged, simple, and exceptionally accurate. They are well priced and I hear MPA's have fantastic warranties.

I've got about 600 rounds through my .223 upper and maybe 200 through my .300 blk upper. No problems on any of the components.
 

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My opinion is pretty simple; Go with the tried & true AR 15 platform, from a good company, Colt, Daniels Defense, Bravo Co, Spikes, etc, if you want a gun to trust your life to.

If you just want something to play with, buy what you like.
 

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Back in 2010 this was an actual debate. In 2014 we are still shooting DI guns and the piston fad is slowly going away.
 

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How about a Mini-14 or Mini-30? I know they are not AR's but they are a reasonably priced piston option that is always consistent in quality. The Sig's are pretty nice as well but they are not what I call bargains!
 
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