Muzzle Brake changing POI

Discussion in 'AR-15 Discussion' started by p35bhp55, Mar 29, 2013.

  1. p35bhp55

    p35bhp55 New Member

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    I installed a Precision Armament M11 on a Bushy 308 ORC. The rifle was sighted in well with the POI about 2 inches above the POA at 100 yards. The rifle was in a vise when the A2 hider was removed there were flats on it to aid in removal. The M11 was threaded on it is snug not tight because I haven't ordered the proper shims. When I test fired it the POI had went down in a straight line exactly 5 inches.
    The scope or rifle wasn't bumped during my work and the scope adjusted up and stayed put, it's hard to imagine the brake changed the bullet flight that much but that's the way it seems.
     
  2. c3shooter

    c3shooter Administrator Staff Member

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    Believe it. different weight, isn't it? Changed the barrel harmonics. Browning uses a sliding weight to tune POI on some of their rifles.
     

  3. jp_over

    jp_over New Member

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    I had a muzzle brake installed on my 375H&H - the gunsmith said I'd have to sight it in again and he was right. I think you lose some velocity with a brake but, regardless of the reason, it can change POI.
     
  4. p35bhp55

    p35bhp55 New Member

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    I'm a believer now just shocked at how much it moved at that range.
     
    Last edited: Mar 30, 2013
  5. jp_over

    jp_over New Member

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    Indeed - it would be interesting to see FPS measurements before & after the brake.
     
  6. c3shooter

    c3shooter Administrator Staff Member

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    It's not just the speed of the bullet. Barrel whips a tad when you shoot. Bullet HAD been leaving barrel on an UP swing. Different weight on the muzzle, different vibration pattern- bullet now leaving on a DOWN swing. You can't see it- too fast for the unaided eye- but the vibration is there. Trust me.
     
  7. MattShlock

    MattShlock New Member

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    5 inches seems like alot though.

    Almost always the pattern opens up a bit too. Guns without muzzle devices are simply more accurate. Forget the proper torque for installing the device for the moment. There is backpressure that affects accuracy. The change could also be due to some related, unbalanced, force.

    I like the Micor breaks because the slots are angled to match the twist of the rifle you put them on and the escaping gases are most efficiently vented. OMG, accuracy-wise, it's like there's no muzzle device on the gun but the Micor works better than standard issue for flash suppresion and at least as well on muzzle flip!
     
    Last edited: Mar 30, 2013
  8. JonM

    JonM Moderator

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    muzzle brakes suppressors flashhiders have no effect on velocity. that only happens in call of duty
     
  9. triggerjob

    triggerjob New Member

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    I think your brake is off center on your barrel. Take the brake off and look into it and see if any lead or copper is shearing off inside of it.

    You replaced a shorter flash hider with a longer muzzle brake. It could be your barrel end threads aren't centered to the bore, or the same thing could be wrong with the brake, occasionally both are off.
     
  10. purehavoc

    purehavoc New Member

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    My buddies long distance target .308 is dead nuts with his custom hand loads . He put a brake on it and it would shoot about 15" high with the same ammo even in a shooting jig he uses to sight stuff in with .. Take the brake back off and its right on . I though that was pretty crazy that it was off that far .
     
  11. triggerjob

    triggerjob New Member

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    Barrel whip will cause this too, but usually on longer thinner "sporter" barrels like on new BARs and those remington auto with the skinny barrels. If your is a heavier shorter barreled baby like is common on AR platforms, you have a miss alignment problem in the machining as I described before.
     
  12. triggerjob

    triggerjob New Member

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    One other thing, have somebody else shoot it and see if the problem is the same. It could be, your pushing the barrel down in anticipation of recoil that is no longer there.
     
  13. jp_over

    jp_over New Member

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    Some muzzle brakes do affect velocity.

    http://www.chuckhawks.com/muzzle_brakes.htm

     
  14. MattShlock

    MattShlock New Member

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    Dude, come'on, that's some crazy MOA right there! Really!?
     
  15. purehavoc

    purehavoc New Member

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    Sorry that was 15" high @ 300 yards, not 100 yards
     
  16. p35bhp55

    p35bhp55 New Member

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    Yeah buddy, I also have mini 14s, know about that barrel movement. But the barrel on this beast is short and heavy, not saying it isn't happening just surprised.
     
  17. p35bhp55

    p35bhp55 New Member

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    OK, there are two posts I'll try to answer here. First I doubt the brake is shaving lead since I shot the best group so far after I put it on. Second I raised the scope 20 clicks, it went right back where it was and stayed there, I think as the round count climbed I would have gotten used to it and shifted back.
     
  18. triggerjob

    triggerjob New Member

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    Mini's have those skinny barrels, also ruger doesn't stress relieve them very well so they twist and turn like mad as they change temp.

    One way to determine if your brake is concentric with the bore is to move it 1\4 of a turn. See where your zero goes. If the zero stays the same don't worry about it.

    Also if you aren't using a bench rest its hard to tell if your equipment isbetter or if you are. Shooting from a rest is the way to test equipment cause it helps eliminate human variables.

    Anyway if it shoots better for you that's great, since that's the point anyway.
     
  19. p35bhp55

    p35bhp55 New Member

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    I don't exactly use a bench rest. I have a framed up stand with a bulls bag and some sand bags the top is notched out so you can lean into it, it's very sturdy but you shoot standing. This happened because when we first started working with sabot shotguns my friends and I went thru several barrels and scopes and lots of slugs. Standing was easier on us.

    Since it's Easter I'm going to give the neighbors a rest on the gunfire and with my schedule It will be next Sunday before I see daylight here again. SWFA is shipping a new scope so maybe by then it will be mounted and I'll be shooting again.

    http://precisionarmament.com/product/m11-muzzle-brake/
    This is a picture of the brake, since it is closed on the bottom, I dunno about turning it sideways, maybe upside down?
     
    Last edited: Mar 31, 2013