Suppressors Grouping Issues....where to start?

[EnterUserNameHere]

Hoping someone here can provide a little guidance as to what may be my issue:

SBR: Self Built 5.56 AR w/7.5" barrel.
Non SBR: Self Built 5.56 w/16" barrel
My Suppressor: HTG Aris 5.56
My buddy's suppressor: Automatic Weapons Company 5.56 (not sure of model)

My non SBR w/no can. Shoots and groups fine
My non SBR w/my HTG can. Shoots and groups fine.
My SBR w/no can. Shoots and groups fine @25yds
My SBR w/my HTG Can. Groups HORRIBLE. All over the target.
My SBR w/my buddy's Can. Groups fine.

Clearly my can is fine. Clearly my SBR is fine. And clearly my SBR is able to shoot fine with suppressors as proven when I use my buddy's can. However, there is something about the combo of my SBR and my HTG can that cause things to go wonky.

From looking down the can, I can't see any sign of baffle strikes.

Any thoughts or suggestions why it would group fine with one can but wildly horrible with a different one?

 

[Zak Smith]

Check the mating of your HTG on the shoulder of your SBR barrel. The first thing to look at with suppressed group problems is its mounting, and that your buddy's can works and it works on your 16 suggests it might be how it's mating to the thread/shoulder on the 7.5" bbl

 

[EnterUserNameHere]

Ok.....total rookie question, here, but ignorance is not bliss in this case.

I assume I'm looking for a nice flush, square mating of the can to barrel shoulder? Will this be obvious, or the short of thing I should be using feeler gauges for.

 

[Zak Smith]

You're looking to see if you can see any light or space between the rear surface of the can and the barrel muzzle shoulder, at any point around it, or if it doesn't look seated exactly square.

 

[EnterUserNameHere]

Thanks. It will be a few days until I can get a chance to take a look. I'll report back. If anything looks suspicious, I'll post some pics.

 

[loveha]

Have you tried other ammo?
My 223 SBR 12.5" 1:8 with Sandman S does 1 MOA (Fed GMM Berger) and 5 MOA (Barnes 62gn TSX). This weekend I'm doing more testing without the can and some other ammo. Want to get a hold of the 70gn Barnes. I tested 5 different match loads plus the Barnes, and it seems to like the heavier stuff.

TLDR, try other ammo, maybe it hates the current combination.

 

[EnterUserNameHere]

I did not try different ammo, however, my groupings at 25yards were 12' or more apart......so basically I was shooting 50MOA!!!! I didn't think that ammo choice could possibly make that big of difference. Worth a shot though.

 

[Mike Casselton]

12' ?
That's twelve feet at 25 yards?
Please tell me you meant to write 12"...
I'm pretty sure you meant 12" because you said 50 MOA.

Sorry man, just busting your chops.
That really does seem excessive for 25 yards.

 

[Viper1973]

12' ?
That's twelve feet at 25 yards?
Please tell me you meant to write 12"...
I'm pretty sure you meant 12" because you said 50 MOA.

Sorry man, just busting your chops.
That really does seem excessive for 25 yards.

I had a POI shift that was 6ft+ at 50y with one of my pistol carbines. Ended up both the barrel threading and the suppressor were out of spec. It did however pass an alignment rod test which made the whole situation wonky as hell. Just saying, feet CAN happen....

 

[Mike Casselton]

That's crazy, but I understand.
A buddy has a RPR that's a great shooter, even with S&B 140 fmj.
It suddenly started throwing shots where it would miss a 12" plate at 100yds. We really thought the barrel was toast.
Turns out the screw that holds the butt stock on wasn't even finger tight. This allowed the rifle to find least path of resistance during recoil and it threw shots wildly.
It also exposed a fundamentals issue that was not noticed until the wild shots.
A little blue locktite and a refreshing of fundamentals and it is fine now.

To continue along this line, another friend has an AR10 that wouldn't shoot better than 5-6" at 100.
Went through a bunch of stuff including ammo changes and found a very loose buffer that essentially replicated the issue with the RPR.
Tightened that up and groups dropped to under 2" immediately.
Strange things, but I can see where some guns can have crazy and hard to troubleshoot issues.

 

[EnterUserNameHere]

12' ?
That's twelve feet at 25 yards?
Please tell me you meant to write 12"...
I'm pretty sure you meant 12" because you said 50 MOA.

Sorry man, just busting your chops.
That really does seem excessive for 25 yards.

Haha Good catch. Typo. 12 INCHES (maybe more) was my grouping at 25 yds.

I'll take a once over on the rifle too just to make sure it is all snug.

For what it's worth....it is a brand new build. I only recently finished it, and in fact, this was the first time shooting it.


Not to get ahead of myself. IF, I find an issue with my barrel shoulder to suppressor "mating", how does one fix this, or is one even able to fix it?

 

[Viper1973]

Haha Good catch. Typo. 12 INCHES (maybe more) was my grouping at 25 yds.

I'll take a once over on the rifle too just to make sure it is all snug.

For what it's worth....it is a brand new build. I only recently finished it, and in fact, this was the first time shooting it.


Not to get ahead of myself. IF, I find an issue with my barrel shoulder to suppressor "mating", how does one fix this, or is one even able to fix it?

In my case I had to have the barrel rethreaded. Sometimes a defective QD mount can also be the culprit.

 

[EnterUserNameHere]

Ok, finally have a chance to take the SBR and can out of the safe. I've attached some photos for the experts to look at.

I also opened up my can and looked at the baffles. No obvious sign of baffle strikes. Dirty, but appears normal on the inside. I'll clean up the baffles and reassemble.

I did, however, notice that like Mike mentioned above, my buttstock/buffertube castellated nut was loose (it too, barely finger tight). I'll crank this back down. I have a hard time believing this was the issue, however, as the rifle would shoot fine without the can and with my buddies can. But, who knows.

From the photos attached, you can see that my can is flush mount....i.e. it doesn't have the extra little bit that sticks out with the threads beyond the back of the suppressor (fwiw, my buddies can did have this little "extension").

Threads and shoulder look normal to me, but I may not know what wrong looks like either.

Suppressor seems to marry up quite well to the barrel shoulder. I don't see any gaps on that.

Let me know if there are any other photos that I can take that could be helpful.

Would it be helpful to snap some photos of the baffles while I have it disassembled?

also, FWIW, my barrel is a 1:7 twist.

 

[c ward]

There is no thread relief at the base of the muzzle threads and its hard to tell from the angle of the picture , there is a gap between the face of the can and barrel shoulder .

 

[EnterUserNameHere]

There is about 1 thread width of relief between the end of the threads and the shoulder. See first photo.

Ive attached some more pics, but I can't see any gaps between the face of the can and the barrel shoulder. It is really hard to take photos of this and not have shadows look like gaps.

 

[Zak Smith]

There is no relief cut on those threads

See detail E

 

[c ward]

I saw the first photo , there is no thread relief . Look at the drawing Zak posted .

 

[EnterUserNameHere]

Ok......having said that, do you all think that the lack of relief is the likely culprit? If so, any way I can test it to find out (add a shim or crush washer)? I'm guessing that the permanent solution would be to have my barrel turned in a lathe to provide some more relief. I would, however, love to see if I could prove that is the issue prior to pumping in $$$ into the barrel.

Also, for what it is worth, my 18" barrel that shoots fine with the can looks almost identical at the threads. The threads end, and then there is about 1/32" of unthreaded portion of same OD as the outer part of the threads. Then shoulder.

 

[lennyo3034]

Try buying a $2 shim from precision armament?

Actually a Surefire shim (the one cut for barrels without relief cut) may work better.

ETA:

Surefire REPLACEMENT SHIM KIT FOR SF3, SFMB & WARCOMP

DETAILS The SureFire SOCOM 556 RC Fast-Attach® suppressor is the world’s most advanced 5.56 mm rifle suppresso

www.bigtexoutdoors.com

 

[c ward]

The threads and the barrel shoulder being the interface between the rifle and the can on a direct thread suppressor it is important they be in spec .

Get in touch with the suppressor manufacturer and determine what spec they use for their threads , there are multiple ones , and take the barrel to someone with the proper measuring tools and have it checked .

TBAC uses the 3A spec and if the thread relief is out of spec what else could be also , and NO a flash hider setting in someone's tool box is not proper tooling .

 

[EnterUserNameHere]

Get in touch with the suppressor manufacturer and determine what spec they use for their threads , there are multiple ones , and take the barrel to someone with the proper measuring tools and have it checked .

Sadly, the suppressor manufacturer (HTG) closed like 8 years ago.

 

[c ward]

You'll need to have the can threads checked also then . Not all manufacturers run 3A threads so it cannot be assumed that is the spec that was used .

 

[Hateca]

Also that drawing is for TBAC stuff not everyone. Not every barrel relief is the same. The suppressor can have a counter bore for the threads because not all barrel threads are created equal.

Quite possible your ammo and the pressure curve with the suppressor is not happy.

 

[Zak Smith]

One way to figure it out would be to have a machinist/gunsmith chuck up the barrel, true it on the bore line, and then measure the runout on the end of the suppressor. This will show right away if it's not straight.

Using witness marks (ie, a pen), you should be able to tell if it's shouldering up against the shoulders themselves, or if it's hitting internally on the thread stub at the base.

 

[EnterUserNameHere]

Finally made it back out to the range to do some more experimenting. The experimenting, however, was not needed. Night and day difference. With the suppressor on, I was not getting 1" groupings (or better) at 25 yards. I was actually getting tighter groupings with the suppressor on than with it off!

What did I do? I did tighten up my butstock nut that was only hand tight. I did an overall clean on the rifle. I did a lot of taking the suppressor on and off.

No doubt the buttstock tightening was a big help. I'm curious if the repeditive suppressor on and off maybe helped "true" up the mating surface a bit? As mentioned, it was a new barrel. Who knows, but honestly, I'm not too concerned about it as it is shooting great now.

Oddly, the POI of the groupings when the can was added shifted all shots 2-4 inches left. Same can on my 16" AR keeps rounds centered left/right, but drops the POI by a few inches.

The left only shift seemed abnormal, but it was rock solid consistent left. Because this SBR will always be fired with the suppressor on, I just rezeroed with the suppressor and am keeping 1" of bullseye on all shots.

This setup seemed to really like the 55gr XM193. I shot some cheap 40gr, some 55gr Blackhills Soft tip and some 62gr XM855. The cheap 40gr and the blackhills 55gr soft tip were close second place to the XM193. The XM855 shot the worst of all the rounds. The XM855 had groupings more in the 2+" range.

Thanks so much for everyone's help here.