Trouble with ar when running suppressor??

[The Duke]

I need some of the knowledge from the great folks here. I built a heavy barreled ar-15 in 5.56 with a white oak armament 2o inch barrel, then had it threaded and had the SAS brake put on so I can run my SAS suppressor. I was shooting it and the groups were great 1MOA or less, if I would exclude this weird one random flier that would be 8 inches low and to the left. It seems to be the first round, but not sure when it is happening due to I was shooting at 200 yards. Oh and I was using Hornady 75 grain match rounds. I do not have an adjustable gas block (hoping to avoid putting on on) and I’m running a H2 buffer. What could be causing this? Do you think I should try to run a H3 buffer to increase the dwell time? I plan to use the gun for varmints, coyotes and maybe a match. Any advice would be great?

[Great-Kazoo]

Possible you are canting your rifle. A degree or 2 can throw it off. Sounds like you're canting left just enough to give you that low & left hit.

http://www.riflescopelevel.com/cant_tests.html

[brutal]

FRP?

[SA Friday]

There are a lot of things that could be causing the flier other than the suppressor. How many rounds on the barrel? If below 200, it could be still settling in. If you aren't sure it's the first round every time you get a flier, it could be a one in ten case with a partially blocked flash hole.

As for the adjustable gas block, buffer weight, and a potential flier... The bullet is gone before timing could cause a flier. Dwell time is the bullet travel from the gas hole to the muzzle. So, adjusting the timing isn't going to effect your dwell time for all intents. The timing on a rifle length gas system is typically optimal with a carbine buffer short of some odd gas port sizing. WOA is really good about that. If anything, I would suspect you are over weighted with an H2 short of running it suppressed all the time. Will it even lock open on an empty mag without the can on it?

You more concrete information to determine why there is a flier. I suspect the gun is over-buffered too, but this isn't causing your issue.

[HoneyBadger]

Good advice above. A few more details would be helpful

Does this only happen when using the can?
Can you find out if it is always the first round in a series? This would narrow things down a little.
What optics are you using?

You should be able to replicate this problem at closer ranges (100 or 50yds), which would make it easier to see your shots.

[The Duke]

I'm using a Bushnell Tactical Elite 6-24 X 50mm ERT. It does not happen when not using the suppressor. It happens randomly in the string of shots when using the suppressor. When running the un-suppressed the bolt locks back on an empty magazine.

[C Ward]

Rifle cant isn't going to cause 8 " fliers at 200 yards even with the gun rolled 90 degs . Check the suppresor and mount real close for baffle strikes , look for copper smears .

[BPTactical]

A couple of thoughts-
The weight of the can has changed the harmonics of the barrel.
I would double check your barrel nut torque, while a lighter torque would not be noticeable unsuppressed it is possible with the additional weight of the can it could be causing slight movement of the barrel if the barrel nut is not torqued to a full value.
Specs say 35-80 ft/lbs IIRC, 55 ft/lbs seems to be a sweet spot.
Check your suppressor mount, make sure it is registering on the shoulder of the barrel and not the muzzle.
Make sure the mounting surfaces of the can/mount are clean, a piece of fouling can get in there, make you think it's tight when it's not.

[SA Friday]

If you are going to be down by Bowers Tactical any time soon, bring the whole set up by and we can look at it for you. We have an alignment rod to check the suppressor and the adaptor alignment, and can check the rest. If not down in our area, Bert is closer.