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Thread: A muzzle device, and its affect on the mechanical accuracy of a barrel

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    A muzzle device, and its affect on the mechanical accuracy of a barrel

    Bear with me on this one guys.


    Considering the importance of a barrel's crown and its ability to evenly disperse gases as the bullet leaves the barrel, so as to minimize initial yaw upon the bullet's exit- how much can a muzzle device on an AR-15 barrel effect the mechanical accuracy of the barrel?

    Granted, this issue may not come into play, or for all I know, even be measurable under, say 500 yards. However, I've been thinking about the topic lately, and have been told that I am not crazy-mental-insane for doing so. Therefore, I'll throw the notion out here for a thrashing.


    For example, take a known brand, higher-quality, AR-15 barrel that is finished with an 11° target crown. This barrel is also threaded for a muzzle device. Which muzzle device, if any, will allow the 11° target crown to do its job and have the least effect on the mechanical accuracy of the barrel? Conversely, how might the given design of a particular muzzle device affect mecahnical accuracy, if at all? Which muzzle devices might have the least affect, and which might have more of an affect?


    I've searched and researched, and all I can find regarding muzzle devices is which ones hide flash the best, and which ones compensate or counter muzzle rise the best. Nowhere have I seen anything addressing how a device might affect accuracy. As for design - and this comes from viewing pictures online, not from holding each muzzle device in my hand - It looks as though some muzzle devices leave the barrel crown complete exposed (i.e. Ops Inc Brake), while others appear to almost completely cover up the barrel crown, and have their own internal crown (i.e. YHM Phantom line). For those models that have their own internal crown, do these snug up against the barrel crown when installed and properly clocked? If not, how big is the space between the barrel crown and the backside of the device's internal crown, and what affect does this have on the bullet and escaping gases ? (hed esplode!)


    This may not be a concern, as most of us probably a) don't have high-end match-type barrel, and b) don't have much opportunity to shoot more than 300 yards. In all honesty, I recently purchased a good barrel. I got to thinking, and wondered if I'd do the barrel a disservice by throwing on just any muzzle device. Chances are slim that this barrel won't see an opportunity to reach out beyond 300 yards. But, pondering notions beyond the scope of reality can be fun and interesting, and sometimes I can take something useful away from the process.

    Please weigh in with your thoughts and comments. Thanks.

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    Army Marksmanship Unit experience has been that a properly installed (there's the rub) muzzle device has little to no effect on a rifle's accuracy.

    A device installed too tightly can put stress on the muzzle as it lengthens the threaded area, causing a "Trumpet bell" effect -- weapon accuracy will fall off.

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    Quote Originally Posted by sinister View Post
    Army Marksmanship Unit experience has been that a properly installed (there's the rub) muzzle device has little to no effect on a rifle's accuracy.

    A device installed too tightly can put stress on the muzzle as it lengthens the threaded area, causing a "Trumpet bell" effect -- weapon accuracy will fall off.
    Hence the importance of installing a muzzle device with a torque wrench to mfg.'s specs and using a thread locker such as Rocksett. Your average Bubba the Builder will just crank it on like he's installing a lug nut with a 4 Way.

    Any muzzle device is going to change the barrel harmonics, which may in turn effect accuracy. But you'll never know which one will or will not increase or decrease group size without trying it. It's going to vary from rifle to rifle and attachment to attachment. No two are going to react the same.

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    Quote Originally Posted by sinister View Post
    Army Marksmanship Unit experience has been that a properly installed (there's the rub) muzzle device has little to no effect on a rifle's accuracy.
    sinister and glocktogo, thanks for replying.


    A device installed too tightly can put stress on the muzzle as it lengthens the threaded area, causing a "Trumpet bell" effect -- weapon accuracy will fall off.
    I have heard that the AMU only hand tightens a muzzle device against a peel washer. The use of a peel washer also helps correctly clock thedevice.

    Quote Originally Posted by glocktogo View Post
    Hence the importance of installing a muzzle device with a torque wrench to mfg.'s specs and using a thread locker such as Rocksett. Your average Bubba the Builder will just crank it on like he's installing a lug nut with a 4 Way.

    Any muzzle device is going to change the barrel harmonics, which may in turn effect accuracy. But you'll never know which one will or will not increase or decrease group size without trying it. It's going to vary from rifle to rifle and attachment to attachment. No two are going to react the same.
    It is interesting you mention barrel harmonics. In my travels on the interweb, I think I may have come across maybe two hiders/comps that metioned something about controlling, quieting, or dampening barrel harmonics.

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    Harmonics are a issue with accuracy. Even browning tried to get in on the action with their boss system. I think that was adjustable to tune for harmonics. If you do a search for .22 LR accuracy you will find in the competition guns a barrel tuner is often used. The same with a bughole tuner that puts pressure on part of the barrel. There is even yet another method that moves a pressure point along the barrel. The kicker with tuning for harmonics is it changes with the ammo. Say you tune it for one and its likley it wont shoot another the same.

    As for brakes and flashiders i wish i could shoot good enough to know. It seems like everytime ive tried to test that it just doesnt work out. Ive wondered how can a brake or a flashider with that first baffle not hurt accuracy. Thats nowhere near a crowns accuracy and there is a small high pressure spot the bullet has to pass through right in between the crown and that baffle. Maybe it all happens so fast thats why they say its a nonissue.

    One thing i do know is that having a barrel reprofiled and or threaded can effect accuracy (harmonics). Dont ask my why but i had a stainless 16" barrel that shot great turned to a custom profile including a M4 notch and when i got it back the barrel wouldnt group near as well with the same ammo. That was even without a muzzle devise on.

    I guess the big question is... Is the air so less dense in front of the bullet that by the time the bullet has hit the trouble spot all there is to effect is the pressure behind it? That would explain why brakes wouldnt have much of an effect since they arnt really breaking a seal with a bullet. Those holes are large enough that the bullet isnt bothered by them. The crown is so important because you dont want to unevenly break the seal on the bullet and caue it to yaw in a direction other than straight.

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    Quote Originally Posted by sinister View Post
    Army Marksmanship Unit experience has been that a properly installed (there's the rub) muzzle device has little to no effect on a rifle's accuracy.

    A device installed too tightly can put stress on the muzzle as it lengthens the threaded area, causing a "Trumpet bell" effect -- weapon accuracy will fall off.
    Great Info!

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    In other words an improperly installed muzzle device can be detrimental to accuracy.

    Improperly can mean = overtorqued, too lose, non-concentric barrel threads, out of round muzzle device, carbon build up in muzzle device, unsquare shoulder on barrel behind threading. I've also seen crash washers do some strange things which is why I don't use them on rifles with magnified scopes. On these I only use precision indexing washers or peel washers or better yet have my barrel turned so that the flash hider/comp times up with no washers of any kind.
    Last edited by Robb Jensen; 04-06-10 at 06:39.
    Chief Armorer for Elite Shooting Sports in Manassas VA
    Chief Armorer for Corp Arms (FFL 07-08/SOT 02)

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    Quote Originally Posted by gotm4 View Post
    .....or better yet have my barrel turned so that the flash hider/comp times up with no washers of any kind.
    Damn... never even knew that was possible, man. Do you basically tighten the muzzle device down first, then pull the barrel out of the upper, turn it until the muzzle device is properly aligned, and then put it back together again?

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    I recently installed a brakeout from aac. My POI was 4" low at 50 yds after installation. Is this to be expected when changing muzzle devices?

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    Quote Originally Posted by mtdawg169 View Post
    I recently installed a brakeout from aac. My POI was 4" low at 50 yds after installation. Is this to be expected when changing muzzle devices?
    If you're going from a flash hider to the Brakeout, which is a hybrid flash hider/comp it's not surprising. The real question is, what difference did it make in group size?

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