Can a muzzle device change POI? ...by a lot?

[Eurodriver]

I had my BCM 11.5" LW w/ T1 zeroed at 200 yards. It had an A2 FH on it.

I put a BattleComp 51.0 on it and shot it at 100 yards today and I wasn't even on paper. I eventually figured out I was shooting over a foot low. The device was installed using a geiselle RR. I might have over tightened a bit, and some google searching says that is a very bad thing. It appears to be grouping alright, but not as good nor where it once was.

ETA: I just broke it loose and there's no way it was overtorqued. I just reinstalled to 20ft lbs, which is about identical to where it was installed previously.

That's the only thing I've changed on the weapon since I last shot it at 200 yards. From what I recall, I believe a 200 yard zero in an AR15 will result in an AR15 shooting high at 100 yards which makes it even more unbelievable I was shooting so low at 100 yards.

Are there other factors at play here, or totally normal due to weight and barrel harmonics changes? I eventually got the zero back up, but I was about 15 MOA low and 5 MOA right. It has me a little concerned the zero shifted that much.

Also, if I did over torque the BC on the barrel last time and now that I've removed the BC and reinstalled to torque spec will the barrel "return" back to normal or is it permanently toast? I didn't go crazy with it the firs time, 30-40ft lbs max.

[JimT]

From my personal experience with two different uppers, a change in muzzle device did alter their POIs.

Upper 1(16" midlength, Aimpoint T1, DD Omega 9.0): Removing a PWS FSC556, and installing a BCM Mod0 compensator altered the POI by 1" left, and 1.5" up at 100 yards. Zeroed for 100 yards.

Upper 2(16" midlength, Aimpoint T1, DD Omega 9.0): Removing an A2 birdcage, and installing a BCM Mod0 compensator altered the POI by 6" down at 100 yards. Zeroed for 100 yards.

Updated to add a third upper.

Upper 3(16" carbine gas, Aimpoint ML2, DD Omega 7.0): Removing a PWS FSC556, and installing an A2 birdcage altered the POI by 2" high, and 2" left at 100 yards. This upper is zeroed for 100 yards.

[Clint]

Did you install it with a crush washer?

[Eurodriver]

Did you install it with a crush washer?

No, I used flat washers until it needed about 3/16 rotation to be aligned. In hindsight, this was probably a little much. Should have had it until it was 1/8 rotation and just snugged it up.

Also, when suppressed, I get about a 5 MOA change of POI to the 8:00 from unsuppressed. Something seems off.

[vicious_cb]

Did you install it with a crush washer?

This. I would just use a shim set to time it then rocksett in place. Its alot of extra worth but its worth it.

[Eurodriver]

This. I would just use a shim set to time it then rocksett in place. Its alot of extra worth but its worth it.

I used a shim set to time it and then rocksett it in place.

[vicious_cb]

I used a shim set to time it and then rocksett it in place.

Then Im not sure how you manage to put 20 ft/lbs of torque on it. Hand tight and rocksett should be enough.

[Eurodriver]

Then Im not sure how you manage to put 50 ft/lbs of torque on it. Using shims and rocksett it shouldnt be torqued to even close that amount. A little over hand tight should be enough.

It wasn't. I rechecked the muzzle device and updated the OP.

[vicious_cb]

It wasn't. I rechecked the muzzle device and updated the OP.

Gotcha. Try just timing it to hand tight with rocksett and report back.

[themonk]

Gotcha. Try just timing it to hand tight with rocksett and report back.

Vicious what's the logic behind this? Both AAC and BattleComp recommend 20-25 lbs on their muzzle devices.

[vicious_cb]

Vicious what's the logic behind this? Both AAC and BattleComp recommend 20-25 lbs on their muzzle devices.

Maybe if you are using it with a suppressor, the extra torque gives you extra insurance your muzzle device will not loosen with heavy can attached.

If you are NOT using a suppressor there is NO REASON to put any torque over hand tight with threadlocker. The logic is ANY added torque will "trumpet" the muzzle and affect accuracy.

[Eurodriver]

I am using a suppressor almost exclusively.

I know that a normal guy can torque about 15 ft lbs with his hands which would be totally sufficient unsuppressed.

That's the issue - enough torque not to come off with the can, but not enough to tweak the rifling or crown.

[vicious_cb]

I am using a suppressor almost exclusively.

I know that a normal guy can torque about 15 ft lbs with his hands which would be totally sufficient unsuppressed.

That's the issue - enough torque not to come off with the can, but not enough to tweak the rifling or crown.

So were you having accuracy issues with or without the can?

[Blak1508]

Maybe if you are using it with a suppressor, the extra torque gives you extra insurance your muzzle device will not loosen with heavy can attached.

If you are NOT using a suppressor there is NO REASON to put any torque over hand tight with threadlocker. The logic is ANY added torque will "trumpet" the muzzle and affect accuracy.

I always torque to 25-30 with all my MDs as per instruction recommendation and instructor recommendation. I have never had an accuracy or barrel problem doing so, on the other hand I have seen hand tightened to thread locked MD's come lose more than once during a course and in one case it blew through the spinning MD and could have caused a big shit storm. I like the "Logic" of torquing properly to value YMMV.

First I clean the thread on both the MD and barrel.
With a crush washer, I hand tighten and from there use a torque wrench and crank it to value and correctly timed. With peel washers I add them until I am hand tight at around the 11 mark and correctly offset timed, and from there torque to value and if done correctly at 12 I am just about or at 25-30 lbs of torque. I thought this was the correct way but maybe I am wrong.

[Eurodriver]

So were you having accuracy issues with or without the can?

Both.

[Blak1508]

You may want to check out the suppressor alignment tool from Geissele. Any strikes on your can ?

[vicious_cb]

I always torque to 25-30 with all my MDs as per instruction recommendation and instructor recommendation. I have never had an accuracy or barrel problem doing so, on the other hand I have seen hand tightened to thread locked MD's come lose more than once during a course and in one case it blew through the spinning MD and could have caused a big shit storm. I like the "Logic" of torquing properly to value YMMV.

First I clean the thread on both the MD and barrel.
With a crush washer, I hand tighten and from there use a torque wrench and crank it to value and correctly timed. With peel washers I add them until I am hand tight at around the 11 mark and correctly offset timed, and from there torque to value and if done correctly at 12 I am just about or at 25-30 lbs of torque. I thought this was the correct way but maybe I am wrong.

All of my muzzle devices are shimmed and tightened with rocksett and Ive never had one come loose. Note other thread lockers are not heat stable, this is why you use rocksett.

[Eurodriver]

How would the suppressor have anything to do with a 15 MOA change in POI when it isn't mounted? Definitely something with the mount. I can see a 6" shift. But to not be on a 24"x24" paper after a muzzle device swap seems really odd.

No baffle strikes.

[Blak1508]

What rail ? Lo-pro block ? If so what manufacture ? I may be reaching but I experienced something similar and I am wondering if it's close to the issue I had

[Eurodriver]

This is a factory BCM 11.5" LW Upper w/ 10" KMR that shot 100% to expectations out to 200 yards. 3MOA or so with a T1 at 200 yards right on target.

The only thing that was done to this rifle between it shooting fine at 200 and off paper at 100 (and about 5-6 MOA groups) was installing a BC 51.0 to ~30ft lbs. This was using the same ammo. I originally wondered if I might have used too much torque, thus distorting the crown/rifling at the muzzle, but after removing the muzzle device there was no way it was overtorqued.

The gas block isn't hitting the rail, I am not getting baffle strikes, I didn't use a crush washer, everything was done right. It's literally just the BC 51.0 on the end of the muzzle as a variable but I am really struggling to believe a muzzle device can change the POI by 15 MOA. Additionally, suppressed, my groups go from POA to 4 MOA at 8:00 which I've never seen this suppressor do on any other rifle (usually 2 MOA max, and always to 6:00)

It has since been re-installed to verified 25 ft lbs (well within AAC's 20-30ft lb spec). I'll try to take it back out this week and see if I can pinpoint what's really going on, but I wanted to ask here and see if anyone had any experience with an issue like this.

[themonk]

This is a factory BCM 11.5" LW Upper w/ 10" KMR that shot 100% to expectations out to 200 yards. 3MOA or so with a T1 at 200 yards right on target.

The only thing that was done to this rifle between it shooting fine at 200 and off paper at 100 (and about 5-6 MOA groups) was installing a BC 51.0 to ~30ft lbs. This was using the same ammo. I originally wondered if I might have used too much torque, thus distorting the crown/rifling at the muzzle, but after removing the muzzle device there was no way it was overtorqued.

The gas block isn't hitting the rail, I am not getting baffle strikes, I didn't use a crush washer, everything was done right. It's literally just the BC 51.0 on the end of the muzzle as a variable but I am really struggling to believe a muzzle device can change the POI by 15 MOA. Additionally, suppressed, my groups go from POA to 4 MOA at 8:00 which I've never seen this suppressor do on any other rifle (usually 2 MOA max, and always to 6:00)

It has since been re-installed to verified 25 ft lbs (well within AAC's 20-30ft lb spec). I'll try to take it back out this week and see if I can pinpoint what's really going on, but I wanted to ask here and see if anyone had any experience with an issue like this.

We can take the can out of the equation as the massive shift is just with the 51.0. Did you happen to shoot it after you took it off the first time? If so did the barrel go back to your original zero?

I have had shifts but never like anything you are talking about. I have a 51.0 but its in the safe waiting on a new upper so I'm not much help there. You may want to pop over to the 51.0 thread that I know you were in and see if anyone else had an issue like you're having with their install.

I would also send battlecomp an email and see what they say.

[Eurodriver]

No, I took it off about 5 minutes before I posted in this thread that I took it off.

I completely reinstalled the BC today. Using flat washers from AAC, got it to right where I wanted it while hand tight. I thoroughly degreased the threads (scrubbed with a brass brush, then degreased to make sure all of the old rocksett was off) then applied a bit of rocksett and using a torque wrench torqued it to 25 ft-lbs.

I'm taking it back out on Wednesday to 50 and 100 yards. I'll see what happens...

This is 25 ft lbs right? I'm not losing my mind?

Out of sheer curiosity - let's suppose I torqued it down the first time to 50 ft lbs, or something excessive like that. Will that cause permanent barrel damage or only cause accuracy issues while torqued? i.e. once the muzzle device is removed will it rebound back to normal?

http://i1328.photobucket.com/albums/w521/6234987u02/IMG_1172_zps56f6dd8e.jpg

http://i1328.photobucket.com/albums/w521/6234987u02/IMG_1171_zpsa8e29076.jpg

[LRRPF52]

With high torque on the muzzle threads, I have seen deformed thread peaks, worse than the pics above. This is usually on badly-machined threads, or when someone is trying to clock an A2 flash hider without the right washers.