Bad group? Check your muzzle device!

[imaguy3]

Put together another grendel for a buddy. He bought the parts and I just assembled. He used a colt receiver set, swapped barrels to this... https://www.classicfirearms.com/ar15...ight-stainless and then he wanted this on the end... http://www.surplusammo.com/products/...tor-gen-i.html

For a scope he also bought the new Bushnell Forge in 3-18 and reused his GGG QD mount. The scope is great and super clear btw (comparing to my HDMRII it's pretty close, almost not worth the cost of the HDMRII)

Anyway we went out to shoot the other day and he zeroed it in without any drama. Then I pushed him out to 440 yards (his first time shooting that far). Using American Gunner he shot a 13" 5 shot group!

Yesterday I took his gun out and set up at 280 (furthest I could in this spot). Sure enough, with American Gunner I shot an 8" group.

Out of curiosity I spun his muzzle device off, just to see.

Then I proceeded to shoot the gun with Gunner, one hole! That's more like it... so then I shot some SST and again it was great. Don't mind the random lonely shots. After I shot the two grendel ammo's I shot my AR offhand just to see because I was lazy and didn't want to walk anymore... I could clearly see the two distinct groups in the scopes ahead of time so I know I didn't fudge them up.

Moral of the story, if you're not happy with your gun's accuracy, just try shooting it bare muzzle first (if it's not).

[A5BLASTER]

That's why I like the accuwasher system so much you can get it timed and not use more then 10 pounds of tourqe and if you need to take it off for whatever reason the washer is reusable like a million times

[imaguy3]

That's why I like the accuwasher system so much you can get it timed and not use more then 10 pounds of tourqe and if you need to take it off for whatever reason the washer is reusable like a million times

There was no crush washer or peel washer used. That particular device he wanted just screws on and snugs against the shoulder. No excessive torque or timing was needed.

He texted me last night saying the central hole looked oblong and out of center to him. I'm going to try and get my hands on it and check it out a little closer. I looked at it quickly and didn't see any evidence of a strike, but maybe just being off center is enough to send the bullet wonky. It's either poorly machined or just affected barrel harmonics so much with the weight on the end.

In my bolt gun for example I had a nice load developed, then as soon as I put the muzzle brake on for my suppressor my loads opened to 1.5" from 0.5" at 100. I had to add .4gr of powder to my load to bring my accuracy back. Prior to that happening on my bolt gun I never would have thought about a couple ounces of weight on the end of the barrel making a huge difference.

[A5BLASTER]

There was no crush washer or peel washer used. That particular device he wanted just screws on and snugs against the shoulder. No excessive torque or timing was needed.

He texted me last night saying the central hole looked oblong and out of center to him. I'm going to try and get my hands on it and check it out a little closer. I looked at it quickly and didn't see any evidence of a strike, but maybe just being off center is enough to send the bullet wonky. It's either poorly machined or just affected barrel harmonics so much with the weight on the end.

In my bolt gun for example I had a nice load developed, then as soon as I put the muzzle brake on for my suppressor my loads opened to 1.5" from 0.5" at 100. I had to add .4gr of powder to my load to bring my accuracy back. Prior to that happening on my bolt gun I never would have thought about a couple ounces of weight on the end of the barrel making a huge difference.

The weight on the end causing issue is also very true.

And if it's the barrels thread section is out of round it is very possible it is causing a strike or some kid if issue with harmonics.

First brake I used I used the crush washer to install it and my groups feel in the trash can, I went round for round with it till I finally just put the thread protector back on it.

Then I got a m4-72 with the accuwasher system and installed per the instructions and thought I would have the same issues as before but didn't.

So after that I started installing all muzzle devices with the accuwasher system and have never had that issue again.

But if the barrel end is out of round I think it will have issues with anything mounted to the end of the barrel.

[imaguy3]

The weight on the end causing issue is also very true.

And if it's the barrels thread section is out of round it is very possible it is causing a strike or some kid if issue with harmonics.

First brake I used I used the crush washer to install it and my groups feel in the trash can, I went round for round with it till I finally just put the thread protector back on it.

Then I got a m4-72 with the accuwasher system and installed per the instructions and thought I would have the same issues as before but didn't.

So after that I started installing all muzzle devices with the accuwasher system and have never had that issue again.

But if the barrel end is out of round I think it will have issues with anything mounted to the end of the barrel.

My buddy brought the comp. into work. I think it's definitely an issue with the comp. The center hole isn't centered on the comp itself. That being said the company refunded him the comp and told him to keep it when he called to tell them what it was doing.. At least they were cool about it.

[03Bullseye]

First Grendel build. Bear creek bbl. 16" m4 contour. Built for daughter. Just tested it. Hornady black eld-m factory. 8" left to right groups at 100 yd. leupold 1-4,hog hunter scope. Got home to clean it and scratch my head for answers. I noticed my Troy brake was very loose. Could that have caused my poor group?

[Wargrendeleagle]

So you recommend the accuwasher system pretty well? I put a vg6 gamma on mine and it comes with a crush washer. To time it I barely had to use any torque to get it pointing the right direction. So little I'm afraid it'll come loose. It seems these are more precision oriented?

[grayfox]

Accuwasher system works. so does using a threaded locknut vice crush washer. Plus a little loctite blue and it will stay put for you.

[imaguy3]

First Grendel build. Bear creek bbl. 16" m4 contour. Built for daughter. Just tested it. Hornady black eld-m factory. 8" left to right groups at 100 yd. leupold 1-4,hog hunter scope. Got home to clean it and scratch my head for answers. I noticed my Troy brake was very loose. Could that have caused my poor group?

maybe... I'd shoot with it off, then tighten it and shoot again... see if there's a difference. There was a definite difference in my buddies gun b/t bare muzzle and muzzle device.

[grayfox]

IMO the looseness of the MB and its shifting to diff positions shot to shot could explain that, anything loose is a problem. My MB's per se haven't caused any POI impacts on or off that I can see... the recoil reduction does aid in grouping however.

[NugginFutz]

I had the same brake on one of my rifles before I decided to forgo them, altogether. Mine was also purchased from Surplus Ammo. It would not thread on completely and did not make shoulder contact, so I had to use a lock nut. I never had any shifting POI issues while I had it on the rifle, and only removed it because I really didn't get much in the way of recoil reduction from it. The only benefit I saw, compared to other brakes, was reduced noise at the shooter's position, but a bare muzzle would do the same. In my mind that basically made it a $50 counter weight, so off it came and on went a thread protector.

As far as the OP's advice is concerned, absolutely should you confirm POA/POI issues by checking without the muzzle device. A good friend of mine was having serious keyhole problems at crazy short distances (25 yards). We removed the $100 muzzle device and his issues disappeared. His problem was obviously caused by bullet strikes, whereas your friend's were likely from the wobbling / off-center bore of his brake. Either way, the check was simple to accomplish and very definitive.

[grayfox]

I would only add one more thing..... if you decide to use one, definitely go with some objective research and get one that has real benefit to you. Bad mfg or cheap engineering, as happens in other pieces/parts, can make for a bad day.