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Old May 28, 2012, 02:10 PM   #1
FordV8
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POI shift with Suppressor

1st. Happy Memorial Day and Thank You to all who have served or are serving!

Took delivery of a Coastal LRT 7.62 Can. (6 mos 4 days from mail date to approved date BTW)

35 yds distance on a 300 BLK AAC 9" barrel, very little shift, quiet, a little heavy but it can handle supers when you want.

125 yds on a SCAR 17S 16" barrel, shooting 168grain Hornady Tap and 175 grain SMKs. POI shift 5" down and maybe an 1" right. No problem, I expected that.

Put the can on a Savage 10 with a heavy 24" Douglas Barrel (which shoots MOA or less without the can) and it shifted 3 FEET down at 125yds. So much shift I ran out of adjustment (Bushnell Elite Tactical 6-24x) before I could get it on paper. Remove the can, dial back to the unsuppressed settings, and 5 shots MOA almost dead center.

Any ideas? Thoughts?

The can is user servicable. No baffle strikes.

I am happy on the one hand... 300 BLK is really quiet and pretty accurate too. SCAR .308 not to shabby. Bolt Gun.... Pffft I'm totally baffled.
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Old May 28, 2012, 06:45 PM   #2
Deja vu
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I am suppressing a 45/70 marlin.

The question I have is how much point of impact shift is considered normal?
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Old May 28, 2012, 07:07 PM   #3
FordV8
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Good question Deja

I dunno. I can live with a few MOA.

I think I might have found a small problem with the Douglas barrel/Coastal LRT combo. It seems even when "gorilla" tight the rear of the can is a tiny fraction from seating on the shoulder of the barrel.

And... the threads are a little looser than the other two barrels. When nearly fully threaded on, the suppressor wobbles more than the others.

Maybe a shim is in order.
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Old May 28, 2012, 07:49 PM   #4
AK103K
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I just got my AAC M4 2000 on Friday. I shot it on two of my AR's over the weekend, an Armalite M15A4(T) and a S&W M&P15 T.

POI with the S&W was pretty much dead on with the red dots zero, with the Armalite, it was about 2" low, and 2" to the left.

I also got a AAC Eco-9 for my Glock 17, and it was dead on. The Eco-9 can supposedly be adjusted for POI, but it wasnt necessary with mine.

300 rounds of 9mm, and 100 rounds of 5.56, no ear plugs, and I can still hear. No more ringing or crickets than usual either!
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Old May 28, 2012, 08:20 PM   #5
FordV8
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Congrats AK.

I have an AAC M4-1000 and love it. It shifts very little and is mostly repeatable. Not bad for a QD can.

I was checking the relief cut on my Douglas Barrel and it doesnt look deep enough. I bet the threads are landing and preventing shoulder contact.

I dont like shims on cans but, I really dont want to send the barrel back to Douglas.
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Old May 28, 2012, 11:45 PM   #6
David Hineline
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I would say your Savage is threaded crooked, did you pull the bolt and look through the bore. as you look through the bore you should not be able to see the silencer being on there at all. If you see it then it is crooked.
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Old May 29, 2012, 08:38 AM   #7
FordV8
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David

I did at the range but, a cheek riser prevents a good clean eye-line down the bore. I plan to remove the cheek riser after work and get a better eyeball.

I think I'll bring home a large metal square too. The Barrel is cylinder (no taper) I bet that will help me eyeball too.
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Old June 1, 2012, 10:09 AM   #8
FordV8
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Update....

Looking through the bore, and using a metal straight edge, has clearly indicated the can was off center. It wasnt snugging up to the shoulder enough to sqaure itself.

A shim appears to "straighten" things out. Literally!

I also have several thin shims for zeroing with the least POI shift.

After my next range trip I'll post the result.

I learned a lesson: Pay more attention to first time can-to-barrel matings in the furure.
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Old June 1, 2012, 10:17 AM   #9
David Hineline
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Industry Std on threads. When cutting threads on a barrel the threading tool can not reach completely to the shoulder. at the end of the threads should be a relief cut a deeper cut that causes a void in the threads.

Now some manuf of silencers put a relief cut in the silencer so it does not need a relief cut on the barrel, some do not, some barrel threaders put a relief cut, some do not.

In your case a flat washer is going to do the trick as it provided a way to not run out of threads before it squares up.

Also measure the exposed threads on your rifle barrel, and the thread depth in the mount on the silencer, if the threads are short on the barrel than the threads in the silencer not filled by barrel will gunk up with blast carbon, if the thread on the barrel is long, the exposed thread inside the silencer can gunk up with carbon and make it hard to impossible to screw the silencer off.

When having barrels threaded have it done by a gunsmith who mounts silencers, not just one who puts muzzle breaks on for hunters.
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Old June 1, 2012, 12:27 PM   #10
Charles S
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David,

That is really good information, that I did not know. When I had a Ruger 22/45 threaded, the gunsmith did an outstanding job, but the threads sit much deeper in the can than they do on my Ruger 10/22 or my Walther P-22. I have to be meticulous about keeping the threads clean to go easily back and forth.

Good advice.

Charles
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Old June 1, 2012, 01:40 PM   #11
FordV8
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David

Thanks so much! That is excellent info.

When talking with my 'smith and SOT dealer, he mentioned the same thing.

So I measured, post near baffle strike though!

.50 inches of threads on the barrel before thread relief shim and .45 inches after shim.

The suppressor has about .60 inches of thread. I'll need to keep those threads clean inside the can.

Thanks again David.
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Old June 4, 2012, 02:29 PM   #12
FordV8
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Update

Went to the range today.

With the "thread relief shim" in place there was very little POI shift.

Went back and forth a few times to verify. It's not perfect repeatability but it's close. POI shift was less than 2 inches every time, and sometimes less.

That amount of shift doesnt bother me. I zero'd with the suppressor and plan to shoot it that way.

Problem solved.... and my groups tightened a little especially with 155 A-Max. This barrel seems to prefer the 155 A-Max so far.

Also shot the SCAR 17s. It seems that POI shift is always 4 or more inches down. I may try some shims to see if I can shift it but... it's a lightweight barrel. I can almost see it sag (LOL!) when the Can is on.
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