POI shift w/MB

[stvaughn]

I have an AA 24" GSR upper. When I install an AA muzzle brake the point of impact shifts 4" right at 100 yards. Is this normal? What might be causing that much shift?

Steve

[mongoosesnipe]

it can happen that's why you don't see brakes on bench rest guns, did you use a crush washer, are the ports in the brake uniform around the brake or are the directional, and did you use a torque wrench and at what setting

[stvaughn]

The AA brake is an asymmetrical design. I used a crush washer and had to thin it out a little to get the brake to line up with the ports in the horizontal upward position. Did not use a torque wrench

[mongoosesnipe]

you will need to shoot the gun at multiple ranges to cheek bullet flight zero at 100 then go to 2-300 on a calm day and without changeling windage shoot a group if it is further to one side than it should be considering wind you have a problem if you cant get out to 2-300 try it with a 50 and 100 shot

[wheelguner]

Adding weight and length to the barrel changes how it flexes and the location of the muzzle at the moment the bullet exits the muzzle.
Check out this site, it will illustrate what happens to a barrel during firing:

http://www.varmintal.com/amode.htm

[frank]

There is a pressure wave that travels in front and behind a bullet. Disturbing this wave can affect the flight of the bullet. A muzzle brake works by redirecting this wave, so it can definately cause a POI shift.

[stvaughn]

I do understand all the dynamics going on with barrel vibrations (well sorta, anyway). I have installed muzzle brakes on other rifles and was just surprised at the magnitude of the POI shift. 4 moa is a bunch of movement.

I will try shooting at longer distances to see if the zero stays where I set it or continues to move right.

Steve

[frank]

Supressors can shift POI that much, so I don't doubt that a muzzle brake can also. As long as it is repeatable, it shouldn't be a problem. If you notice that it affects your accuracy, I'd try a different brake.

[NugginFutz]

Supressors can shift POI that much, so I don't doubt that a muzzle brake can also. As long as it is repeatable, it shouldn't be a problem. If you notice that it affects your accuracy, I'd try a different brake.

This is one of the reasons I prefer a symmetrical brake. If the escaping gasses are leaving in a uniform pattern, then minimal interference should be realized. Another factor is how centered to the bore the brake is. If off-axis, then the bullet path can be influenced at the muzzle. An off-axis brake can be caused by either machining issues with the brake, or even the barrel threading. Fortunately, this seems to be a rare situation. Just not rare enough.

[Buster]

I replaced an A2 birdcage on my 7.62x39 16" AR with a BRO brake. POI was high and right about 3" @ 50 yards.

[SG4247]

I have many brakes and a YHM supressor. All of these muzzle devices have been tested on my competition ARs to determine suitability of recoil, and mean group size for my calibers of .243, .260, 6.5G, 6.5L, and .308 mostly with custom loads.

With my favorite brake, i have seen as much as 8" increase in POI @ 100 yds over no brake. I have even tested theses installed upside down.

I will not ever use a crush washer on my barrels. I only use a JP stainless ground locknut or steel shims with these devices. A cupped crush washer is very hard on the small shoulder of the barrel threads, especially if you take it on and off often like I do - to clean the barrel.

My testing indicates:
1. All these devices changed POI depending on design type used. You must zero the rifle with the brake installed and clocked.
2. Group size can be affected in both a positive or negative way, depending on type of device and rifle/caliber used.
3. They will group in a repeatable way, if they are indexed to the muzzle in exactly the same orientation consistently.
4. Some reduce recoil, muzzel rise and dust signature significantly, while others not as much.
5. They are loud as hell.
6. They need to be secure to barrel, during a match with high barrel temp, I had one come loose and caused a miss.
7. You have to do research and test the device on your rifle, with the intended ammo, to determine if it provides the desired results.

There are some great articles online where muzzle brakes have been tested.

Hope that helps.

Glenn