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Stone
05-24-2011, 1:25 PM
When firing a high powered round out of a barrel that is too short to allow all the gasses to fully expand, there will clearly be a lot of expanding gasses billowing out around the bullet as it immediately leaves the barrel.

I'm concerned with these gasses having an influence on bullet accuracy. I would suspect that perhaps a higher twist rate would become important to compensate, but I'm mostly curious about the effect that different muzzle attachments have.

Flash suppressors, muzzle brakes and comps...what is their effect? Positive? Negative?

r6raff
05-24-2011, 1:43 PM
When firing a high powered round out of a barrel that is too short to allow all the gasses to fully expand, there will clearly be a lot of expanding gasses billowing out around the bullet as it immediately leaves the barrel.

I'm concerned with these gasses having an influence on bullet accuracy. I would suspect that perhaps a higher twist rate would become important to compensate, but I'm mostly curious about the effect that different muzzle attachments have.

Flash suppressors, muzzle brakes and comps...what is their effect? Positive? Negative?

I have never heard of a muzzle device effecting accuracy to a degree where it would be noticeable. Generally a Brake or FH will do more for redirecting flash and diminishing or directing muzzle rise and recoil. I remember reading something about a particular M1 garand muzzle device that noticeably effected accuracy but I think that is a rather isolated anomaly.

I think the short answer is no, but I may be wrong, we'll see what some of the really knowledgeable guys say.

Stone
05-24-2011, 8:06 PM
Thanks for your input r6raff. I am bumping this in the hopes of getting some more feedback. Here are some quotes I have found on the subject from scanning the internet:

Maybe not a flash-suppressor, but a muzzle brake might. There is evidence that gas expands between 7,000-9,000fps. As the bullet exits the barrel the gasses begin to pass it, since the gasses are able to travel at a greater speed.

When these gasses hit the 'plate' surfaces of the brake, the bounce of some gases are directed towards the bullet. It is thought that these gasses effect the yaw of the bullet, causing de-stabilization.
Due to the bullets rotation, the bullet will be restabalized, but there's a chance this won't happen at a constant distance from the muzzle. This would cause diminished overall accuracy.

Due to the larger exit diameter of the flash-hider's design, the effects of bounced gases are much less, but still present.

In the excellent and fascinating book Rifle Accuracy Facts by Harold R. Vaughn [Precision Shooting Inc. 860-645-8776], it is stated that bullets are affected by muzzle blast for fifteen calibers forward of the muzzle (page 24). Properly designed muzzle brakes re-direct the expanding gases away from the bullet flight path and enhance accuracy and precision. I suspect that some flash hiders provide some degree of gas redirection and affect accuracy.

Good question. The NM mod to the flash suppressor is done by reaming to enlarge the bore. The reamer used is tappered so the front is larger (.406"). One of the effects of the larger tappered bore is that it allows gasses to escape around the bullet with less disturbance. Gasses accelerate much faster than the bullet when it exits the muzzle of the barrel. Some gas is expelled through the slots in the suppressor while some are held in by the webbs. The tappered bore allows the gas to disburse much faster than in a standard suppressor resulting in less effect on the stability of the bullet.

I was very surprised to see how much the vertical stringing was magnified with nothing on the muzzle. In fact, the heavier the flash hider, the less vertical stringing appeared. It was strange though, the heaviest flash hider that decreased the vertical stringing also appeared to introduce some horizontal stringing.

We discovered after the AWB just how accurate a plain muzzle AR can be with a 11 degree crown. All of my competition ARs have plain muzzles with 11 degree crowns. I visited with a AMU shooter once about their setup as they must use “looks like” issued with a FH. He told me they go through the box and fined ones that are machined square and that after a boat load of experimenting over the years the FH is installed hand tight only for best accuracy, USMC guys said the same. You may notice after a stage the AMU/USMC guys will reach up and check the FH to make sure it is still hand tight. This is for issue type FH ( flash suppressors ) only. I have tried several muzzle devices and never found one that would shoot as well as an empty muzzle on my AR rifles.

Interesting page here on muzzle tuners (http://www.varmintal.com/aeste.htm):
CONCLUSION.... For lowering the amplitude of the high frequency vibrations, it appears that even an "out of tune" tuner is better than no tuner at all.

While some at Springfield, Inc. (the commercial firm, not to be confused with the US Government's now-closed original Springfield Armory) say that the M14 flash suppressor "does affect harmonics of the M1A most favorably." This is contrary to all my experience, which indicates that the flash suppressor does nothing for accuracy. It does change impact (whether on or off), but does not affect accuracy.
--Clint McKee

The cone type flash hider definitely degrades accuracy to some extent (just how much it will affect your individual rifle, only testing will determine). This is likely not only because of additional weight on the muzzle end (much as the an attached bayonet affects accuracy), but may also be due to the design of the device. Apparently most snipers discarded the flash hider in actual use for this reason, and few actual combat photos seem to show the device installed. The T37 replacement is likely to affect accuracy less, although I have not tested one (my M1D has the cone type) but the design was meant to be an improvement and apparently resulted from the many complaints from the field about the cone type.

Jim R

I haven't used the T37 "prong" type so I can't speak to it. I do however have the M2 Cone ( heavier type, USMC) on my M1-C & it too seems to degrade accuracy compared to leaving it off. ( sure looks cool though!)
I have been using a smith enterprises muzzle brake with no ill effects to accuracy at all. In fact it completely eliminates all muzzle rise (literally) & seems to aid in flash suppression as well.

killshot44
05-24-2011, 8:55 PM
My experience with a Levang Comp, an SJC Titan brake, a Miculek and a BattleComp showed only a minor shift in POI with the Levang only. The others had no change in POI. This was all on a 20" HBAR chambered in 5.56.

My target guns all have naked target crowns, no brakes or comps allowed in NRA matches. (though we won't turn away guys with brakes, but they do get put on the end of line)