Point of impact shift/suppressors

This afternoon, while doing a functional check on an 10.5 inch suppressed upper, I encountered a weird poi shift that I can not figure out.

The rifle was first zeroed using 55 grain wolf steel cased ammo at 15 then 25 yards . I did not use optics and the initial groups were shot unsuppressed , open sights using a match bus and magpul mbus front sight. POI was about 1.5 low at 15 yards, then at POA at 25 yards. Everything was okay until I installed an older AAC M4 2k suppressor with an 18T flash hider.

The groups started shooting about 8 inches to the right. With some rounds making keyhole prints on the target at 15 yards. I was thinking a loose mount or can, maybe a dreaded baffle strike. But none of that happened.

I took off the can and installed another m42000 mod7 can. It shot at POA again. I switched back, it shot all over the place again. After shooting about 40 rounds, the groups started to shoot closer to POA and iT got tighter. At 60 rounds, it was shooting at POA just like the other can.. No baffle strikes, nothing loose, but I can't figure out the lousy groups and keyholes.

When I got home, I carefully examined the older can and can not see anything wrong with it. Mounts checked out okay, ammo was fine. I am stumped.

I'll shoot it some more with optics and if it gives me random groups again, I may have to send it back to AAC.

Anyone of you experience anything similar? Btw, it also shot bad groups with lake city brass cased ammo, after 60 rounds... It's shooting normal.

It is normal to encounter a POI between suppressed and non suppressed shooting . Usually, suppressed shots will print slightly lower due to the added weight to the muzzle. My LE6920/AAC M42K mod 7 will about an inch low at 100 yards. Same thing for most other rifles.

But an 8inch deviation and keyholes at 15 yards, no keyholes at 1 yard. Then it all went away. Strange.

SCARCQB said:

It is normal to encounter a POI between suppressed and non suppressed shooting . Usually, suppressed shots will print slightly lower due to the added weight to the muzzle. My LE6920/AAC M42K mod 7 will about an inch low at 100 yards. Same thing for most other rifles.

But an 8inch deviation and keyholes at 15 yards, no keyholes at 1 yard. Then it all went away. Strange.

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Were your groupings about the same?

No signs of any deflections off the end cap

I can't think of any other way a suppressor would destabilize rounds except for an impact.

No clue aside from a strike or something not being concentric to the bore.

The fact it stopped, is intriguing to me. Figured it should be constant.

ericoak said:

Were your groupings about the same?

No signs of any deflections off the end cap

I can't think of any other way a suppressor would destabilize rounds except for an impact.

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I can't explain it. I even stuck a fiber optic camera inside the can to check for baffle strikes, any signs of projectile rubbing or contacting the baffles or end cap. No such thing. But the first 60 rounds impacted 3 inches low and 7-8 inches to the right at 25 yards. No can, it was dead on. Another can, same gun and 18t adapter, dead on as well.

SCAR, if you want to try it again later today, I'll bring out some brass-cased remington rounds - see if those behave the same...

Maybe it's the way that powder burns and the available oxygen inside the can the first magazine or 2 destabilizing the rounds???

Really have no clue if that's even a possibility, but I'm trying...

BradMacc82 said:

SCAR, if you want to try it again later today, I'll bring out some brass-cased remington rounds - see if those behave the same...

Maybe it's the way that powder burns and the available oxygen inside the can the first magazine or 2 destabilizing the rounds???

Really have no clue if that's even a possibility, but I'm trying...

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Save the ammo for now, I'm trying to arrange for some trigger time at a private range. I'll PM you. Bring some subsonic blackouts as well.

Cost of ammo, expensive..... Suppressed Automatic fire and actually hitting your targets . Priceless.

SCARCQB said:

Save the ammo for now, I'm trying to arrange for some trigger time at a private range. I'll PM you. Bring some subsonic blackouts as well.

Cost of ammo, expensive..... Suppressed Automatic fire and actually hitting your targets . Priceless.

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I'll have to dig up some factory subsonic 300BLK, only got what I've rolled out lately. 225gr Hornady BTHP Match doing just under 1050fps.

Fun to plink in the backyard and not HAVE to have ears on, still not .22 subsonic quiet though. Might be time to invest in a can...

BradMacc82 said:

I'll have to dig up some factory subsonic 300BLK, only got what I've rolled out lately. 225gr Hornady BTHP Match doing just under 1050fps.

Fun to plink in the backyard and not HAVE to have ears on, still not .22 subsonic quiet though. Might be time to invest in a can...

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Inbound is an AUG suppressed barrel group in 300 BLK. Allows caliber change from 5.56 to 300 BLK in less than 10 seconds without tools.

That should be fun. No heavy can sticking out like a construction crane.

This is a known problem with the 18T cans and it's why the 51T design came out. The springs on the 18T are shot, send it to AAC for new ones. Apparently they wear out with use. See http://forum.snipershide.com/snipers-hide-suppressors/37556-aac-7-62sd-poi-6-8-off-2.html

SCARCQB said:

Inbound is an AUG suppressed barrel group in 300 BLK. Allows caliber change from 5.56 to 300 BLK in less than 10 seconds without tools.

That should be fun. No heavy can sticking out like a construction crane.

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Where did you find the barrel group? i've been looking for a 300 blk barrel for my aug for awhile, I thought they were vaporware, also if you don't mind could you tell me how much you paid?

bcr229 said:

This is a known problem with the 18T cans and it's why the 51T design came out. The springs on the 18T are shot, send it to AAC for new ones. Apparently they wear out with use. See http://forum.snipershide.com/snipers-hide-suppressors/37556-aac-7-62sd-poi-6-8-off-2.html

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This is what I was going to say as well.

I have also seen carbon build up on the Muzzle Device Splines which can cause some weird harmonics and possibly Projectile Contact, a Fracture on a Spline can also cause issues.

If anything I would remove the Muzzle Device and run some Wipe Out in the bore and then run a Crowning Ball on the Muzzle. Degrease the Threads and Install a NEW Muzzle Device.

How many rounds through the Barrel? Could the Throat be shout out? I have seen guns with BAD throats shoot like crap will they were warm and fouled.

The m42000 in question has less than 150 rounds through it, the spring isn't worn out. Nothing came loose.

I did notice that the older aac cans had smaller bores as compared to the newer version. It Also created more gas , increased cyclic rates. Another sot told me that this occurred with a bunch of pd guns.

I'm sending it back to aac. I'm still getting keyholes even on a new noveske barrel and good ammo.