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Discussion Starter #1
I shot the target you are about to see yesterday at 200 yards with an AR with a Seekins Precision 10.5" barrel, a Leupold VX-6 3-18x scope and a Vortex Razor Gen II 1-6x scope, a Trek T suppressor (that kept coming loose), and an ATF approved SBR lower. I have tuned the first stage of the Geissele SSA-E trigger to my preferences. I'm leaning toward a Geissele National Match DMR - I really like all the adjustment. Anyway...

Here's a pic, actually two pics of the gun. There are, or have been two versions with the only difference being the handguard. The first pic is with the 12" MI SP handguard, and the VX-6 scope.



Fortunately, I had a pic of the other version and it not only had the Razor scope on it but the other handguard as well. I went from this version to the SP version (above) and now back to the one shown below or at least a version of the one shown below. This is going to evolve into a sidebar - can't help it, but,

I try to use JP Enterprises adjustable gas blocks. I've used Wilson Combat, Syrac gen I and IIs, SLR, and Seekins Precision adjustable gas blocks - they all seize up - all of them, repeatedly seize up - all but the side adjusting JPs! In addition, the JP side adjust is far easier to assess than the end adjust types, DEPENDING ON THE SPECIFIC SET UP. I replace the set screws that come in the JPs with Allen head cap screws. You can apply more force, the heads won't strip out as some set screws have the tendency to, it's easier to get the larger Allen wrench in the larger Allen head cap screw. The JPs have never seized up on me.

Now about that "...depending on...". If the handguard covers the gas block, it can be difficult, and if a suppressor is in place it can be practically impossible to adjust a gas block from the front. Likewise with the wrong handguard, it can be impossible to adjust the JP side adjust because the adjustment screw is covered by the handguard. Which brings me to why I switched back to the MI SS type handguard. Although in the pic below, the handguard does not cover the gas block, I have one coming that will. The reason I want a longer handguard is the short ones don't give you much room for your support hand, and they give no protection from the hot suppressor. It turns out that in the longer MI SS handguards one of the holes lines up right at the adjustment screw in the JP block. You simply poke an Allen wrench through the hole and adjust the gas!

So this gives me the option of a short handguard as shown, a longer one that would extend close to the suppressor, a longer one that would cover about half of the suppressor, and yet a longer one that would cover almost all of the suppressor. The only reason I don't use that last one is because you can't install, remove, or tighten the suppressor - there's not enough suppressor exposed to grip it.

Since all of these mount the same, all that's required to change one out is to remove a set screw on the bottom, loosen the lock ring, and screw off the handguard. The next one goes on the same way.



Oops, I didn't intend to get so sidebarred :embarassed: On to the shooting part.

The pic below is one of the targets I shot yesterday at 200 yards. I shot two different types of ammo, different brands but both Serria MK BTHPs, one was low velocity, one was significantly higher velocity. Basically the left doggie was shot with the low velocity and the right doggie with the higher velocity. There are 3, 4, and 5 shot groups - just depended on what ammo I had left at this point. Both bodies and the head of the right doggie were shot with the VX-6 3-18x scope. The head of the left doggie was shot with the Raxor Gen II 1-6x.

It is interesting that the head shot on the left doggie, shot with the 6x scope is almost 3 times larger than the body group shot with the 18x - 18x is 3 times bigger than 6x - wonder if there's a message there???



The average group size for the three groups shot with the 18x is 0.43 MOA. And the 0.9 MOA group shot with the 6x isn't bad!

I am convinced that some one with younger/better eyes could do better than this - I could see eye issues and just had to deal with them.

So in conclusion, with the right scope, right ammo, and right barrel, SBRs seem to give up no accuracy as compared to their longer counterparts. However, this was a windless day; on a windy day, the longer barrel should be observably more accurate due to the higher velocity and shorter travel time.
 

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Same.
153 yard shot using an 8" .300 blackout with a XCaliber can on it. Shot right through the heart. No accuracy issues there.
 

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Discussion Starter #4
I can tell you this they shoot MOD=Minute of Dear at 150 yards. A few years ago I dropped a deer at 120-150 with my 10.5 inch Noveske build used a 223 60 grain soft point spitzer reload, using a aimpoint Micro. I was using a suppressor also. Deer was DRT.
Thanks for that!
 

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Discussion Starter #5
I can tell you this they shoot MOD=Minute of Dear at 150 yards. A few years ago I dropped a deer at 120-150 with my 10.5 inch Noveske build used a 223 60 grain soft point spitzer reload, using a aimpoint Micro. I was using a suppressor also. Deer was DRT.
Rob,
Any idea what velocity that 60 gr bullet left the muzzle at? Thanks!
 

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Discussion Starter #7
Tangle unfortunately no.
Could you be more specific? :tongue:

Now that you have a chrono, could you chrono what you shot the deer with and PM me? Thanks if you can, no problem if you can't.
 

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Could you be more specific? :tongue:

Now that you have a chrono, could you chrono what you shot the deer with and PM me? Thanks if you can, no problem if you can't.
I may still have some left, and I will let you know if I find it and I will chrono it.
 

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Don't PM him, post it. I want to know also.
 

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With scopes involved I expect the same accuracy as with long barrels or even better since the time in barrel is less for you to disturb the shot. The old short barrels are inaccurate mantra is from the days of iron sights and the associated short vrs long sight radius equation. Short barrels with iron sights are hard to align. Longer barrels and the longer sight radius is much easier to align.
 

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Shorter barrels can be more accurate. With a longer barrel and everything else equal it is more likely to bend/twist/contort/flex under all that pressure, compared to a shorter barrel.
 

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Discussion Starter #12
Just a word about short and long barrel accuracy. Notice you don't see any military snipers, long range shooters/hunters, bench, or precision shooters using short barrels - they all use long barrels. There's a couple of reasons for that. One, in the case of snipers and hunters, the longer barrels yield more velocity and hence delivery energy on the target, and the longer barrel extends the effective range, but that doesn't explain why bench, long range, and precision shooters don't use short barrels. They don't because they get more accuracy from longer barrels. Again, the velocity is higher, time of flight is shorter, wind has less effect, there's less drop.

However other than long range shooting, it may be true that shorter barrels are more accurate, but it really depends on the characteristics of the barrels rather than the length. For example my short pencil barrels are less accurate than my standard profile longer barrels and the thin barrels drift like crazy. I have not been able to document that my heavy short barrels (10.5") are any more or less accurate than my heavy longer (16" & 18") barrels.

Still I suspect the shorter barrels are a bit more accurate for the reasons others have stated - less barrel flex for a given barrel profile. But, there's another thing that may introduce inaccuracies in the shorter barrels. That is the fact that practically all factory ammo is designed for use in a 24" barrel. Because ammo manufacturers compete with each other, they would want their ammo to be as accurate as possible within manufacturing reason and would adjust their loads to produce the best accuracy from a SAAMI required 24" test barrel. When we shoot that ammo in a much shorter barrel, we don't know how the ammo will behave since it is way out of its design length.

For example, I shot some Winchester premium type ammo, maybe PDX, but the spec'd velocity was 2750 fps. Out of my 10.5" heavy barrel it chrono'd at just barely 2000 fps. All other ammo of the same weight or a bit heavier clocked 200 - 300 fps faster!

There'a a lot more to it than just barrel length and rigidity.
 

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Discussion Starter #14
IF you put a red dot on each of them it would start to even things up. For iron sights, longer will have less sight radius error, but that's a sight issue, not a accuracy issue due to barrel length.

But the comparison could be the long revolver pictured against a 7.5" AR-15 SBR. All I'm saying is there's more to it than barrel length.
 

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A short barrel has fewer nodes and antinodes through which barrel harmonics (and the resulting barrel whip) cause changes on POI. A short, stiff barrel can be very accurate....as long as you have enough barrel length to get efficient powder burn and the resulting velocity to keep the bullet's time of flight short so that other forces (gravity and wind being chief among them) have less time in which to act upon the bullet. As with anything else, there is a point of diminishing returns in both longer barrels increasing velocity and shorter barrels increasing effective stiffness. The "ideal" point between those two depends on the cartridge, the load, the type of barrel, and what sort of day the girlfriend of the guy making the barrel was having.
 

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Discussion Starter #16
A short barrel has fewer nodes and antinodes through which barrel harmonics (and the resulting barrel whip) cause changes on POI. A short, stiff barrel can be very accurate....as long as you have enough barrel length to get efficient powder burn and the resulting velocity to keep the bullet's time of flight short so that other forces (gravity and wind being chief among them) have less time in which to act upon the bullet. As with anything else, there is a point of diminishing returns in both longer barrels increasing velocity and shorter barrels increasing effective stiffness. The "ideal" point between those two depends on the cartridge, the load, the type of barrel, and what sort of day the girlfriend of the guy making the barrel was having.
Even considering the nodes, if a bullet load is developed to work with the nodes, the accuracy may actually be enhanced. You will never see a precision shooter shorten his barrel to get better accuracy.

The other thing that one has to wonder about in shorter barrels is the reduced stabilization of the bullet due to reduced velocity. Bullet stability is primarily governed by the rate of spin. When a load is developed for a 24" barrel as I mentioned in my previous post, it has sufficient spin to stabilize the bullet. When that same bullet is shot in a shorter barrel, its muzzle velocity can be dramatically affected as illustrated by the Winchester load I described. Also, the spin rate is proportionally reduced by the reduced velocity. Since the spin is responsible for stabilizing the bullet in flight, if the spin gets too low the bullet won't be stable and accuracy will suffer.

An excellent example of this is the subsonic 300 blackout. The 200+ grain bullets fired at subsonic velocities are notoriously inaccurate. Savage Arms cancelled their 300 Blackout bolt gun project because no matter what twist rate or barrel length they used, they could not get the accuracy out of the subsonic bullet. You take that same 200+ gr bullet and fire it as a full power supersonic load and the accuracy is fine.

There's a lot more to it than just barrel stability. If shorter barrels were truly more accurate, every precision shooter would be changing to them.
 

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I would counter that a short barrel can be inherently more accurate - even when a load is tuned to a specific barrel, there will always be a loss of accuracy due to the minor shifts in POI, and longer barrels will generally have higher amplitude vibrations, which results in greater POI shift. The reason that benchrest and other precision shooters don't shorten their barrels radically is the trade-off that I mentioned earlier, and that you mentioned in your reply...velocity (linear AND rotational) is important to accuracy. If there was a way to get 4000 FPS out of a 4" barrel that was 4" in diameter, that's the only thing that benchrest shooters would use - but it takes time and space to complete your powder burn and accelerate a bullet - and if you don't have huge barrel whip issues, then the extra velocity from a longer barrel trumps the very small increase in precision that the shorter barrel and accompanying reduced vibrations would bring.
 

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Discussion Starter #18
... The reason that benchrest and other precision shooters don't shorten their barrels radically is the trade-off that I mentioned earlier, and that you mentioned in your reply...velocity (linear AND rotational) is important to accuracy.
But doesn't that say a longer barrel is more accurate because it can produce a higher muzzle velocity and hence more bullet stability?

... If there was a way to get 4000 FPS out of a 4" barrel that was 4" in diameter, that's the only thing that benchrest shooters would use
Has that ever been tried? If not, how do we know a 4" barrel would be more accurate than a 24" barrel?

... but it takes time and space to complete your powder burn and accelerate a bullet - and if you don't have huge barrel whip issues, then the extra velocity from a longer barrel trumps the very small increase in precision that the shorter barrel and accompanying reduced vibrations would bring.
So how do we measure that very small increase in precision from a shorter barrel when the longer barrel is more accurate due to the extra velocity? Doesn't that say that if we shoot the two against each other, the longer barrel will shoot more accurately due to the extra velocity from the longer barrel?

We know that guys that are interested in accuracy from 50 to 1000 yards use long barrels. We also know that shorter barrels produce less velocity and less velocity means more drop, less spin and hence less stability, longer travel times and hence more wind drift.

But, look at all the things we've discussed that can affect accuracy. Remember me saying it's not as simple as just barrel length? I think we've proved that.
 

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Neither short nor long means accurate in and of itself....but if we had the technology to remove barrel harmonics from the equation we would decrease the group size.

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Some guy from rugerforum.net did the math, I am not trying to take credit for it. With a shorter barrel you have less velocity, so you can increase the twist rate, which will also determine your ideal bullet weight, which will stabilize the bullet:

"Internal ballistics have a direct impact on external ballistics. As you probably know, factory ammo is loaded very close to SAAMI max pressures. If you increase bullet weight you have to reduce the powder charge or chamber pressure will skyrocket. This is proven by looking in any reloading manual. When a heavier bullet is used with a lighter powder charge, velocity is reduced. Bullet spin rate is a product of muzzle velocity and the barrel's twist rate. The higher the velocity and/or the faster the twist rate, the higher the bullet's spin rate will be. The formula for spin rate is: 12 divided by twist rate times velocity (in fps) times 60 (number of seconds in a minute) = RPM. As an example: the above 150 gr bullet with a MV of 2820 fps and a twist rate of 1:12 ... 12/12x2820x60=169,200 rpm. According to my references, 170,000 rpm is the optimum spin rate for a 150 gr .308 bullet ... very close to .308 Win specs.

With a 16.5; barrel, velocity with the same 150 gr bullet is reduced to 2584 fps. With the faster twist rate of 1:10, here's the results: 12/10x2584x60=203,040 rpm. As you can see, the faster twist rate more than compensates for the loss of velocity, making a 150 gr bullet too light and will & over stabilize

Using QuickLOAD, I found the best bullet for your 16.5" barrel and twist rate. It is a 162 gr bullet (not common) so the closest common bullet weight would be 165 gr. With factory 165 gr ammo loaded to 2700 fps from a 24" barrel, your 16.5" barrel will develop about 2440 fps. 12/10x2440x60=175,680 rpm. The optimum spin rate for a .308 165 gr bullet is 182,000 rpm, which is very close to the calculation ... a 162 gr is almost perfect."
 
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