9mm upper - impact shift with suppressor

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  • LArhino

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    Jan 13, 2011
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    Ruston
    I have put together a 9mm SBR upper for suppressor use (being used on a registered SBR lower). Barrel was supplied by ADCO and is 4.5" and threaded 13.5 x 1 LH with a 1 in 10 inch twist rate. It is being used with an AAC TI-rant.

    I know that most firearms will exhibit some impact shift with the use of a suppressor. However, I am getting a 3" low and 3" right point of impact shift at 15 yards and keeps getting larger as you move out. It has the same shift with 115 gr ammo as well as 147 grain ammo. It also groups consistent with and without the suppressor.

    Does this sound reasonable?

    Thanks for any input.
     

    noob

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    Mar 18, 2008
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    Do you plan to shoot it Unsuppressed? If not I would just zero it with the suppressor on. I have a 4.5 inch barrel from tros and using an AAC Evo with zero issues, but at the same time, I can't shoot it without the suppressor since the handguards are 9 inch. And to ease install, (I used to use it with a tirant 45) I added a tros 3 lug adaptor, and an AAC TRIAD mount.
     

    beauxdog

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    Sep 18, 2007
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    You sure that your not getting baffle strikes? It sure seems that something is out of alignment. Look at the end plate real close.

    Beauxdog
     

    LArhino

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    I would like to be able to shoot it suppressed and unsuppressed. As it is now, I have flip up sights for when unsuppressed and an optic when suppressed.

    I have modified a 5" flash hider to fit when shooting unsuppressed to protect the inside of my hand guard as well as my hand. I have tried shooting without the flash hider and it shoots the same as with the flash hider installed.

    Baffle strikes is what I am concerned about. Unfortunately this is an older ti-rant that can't be taken apart so I can not closely inspect the internals. Looking from the piston end there appears to be some areas that look as though something is brushing but not sure.

    I thought the heavier bullets were possibly not stabilizing so I tried the 115 grain. They shot to the same spot as the 147. I was at the point that I figured something was out of alignment but I wanted to see if anyone else had a similar issue with a short barrel 9mm/suppressor set up.

    I was hoping not to have to sink more money into the project but that is how things go.

    I had read that ADCO did good work so I purchased from them. Any other options for short 9mm barrels out there without much of a lead time?
     

    Kurt D

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    Jan 19, 2010
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    It's ok I saw about the same shift on my SBR mp5 clone and Ti-rant. No baffle strikes here either. Are you using the fix barrel spacer? What I did was with the spring assembly installed I would rotate the suppressor until the POI matched or was as close as possible to POA (assuming zeroed without the suppressor, adjusting POI with this method is in the AAC manual). Once I was were I needed to be I noted were the arrow and "ON" on the piston was in relation to the markings on the suppressor tube. When I installed the fix barrel spacer I made sure everything stayed in the same position. On mine POI and POA matched suppressed or unsuppressed once everything was adjusted; that's not always the case but it can help where it's "close enough."
     

    Rainsdrops

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    If you do not have baffle strike, and im think you dont, because you didnt mention the suppressors exit hole, being out of round, you are experiencing a high amount of blowby in the last baffle or 2. Blowby is the hot gas that beats the bullet through the hole. Too much will cause a shift. Contact the manufacturer
     

    LArhino

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    I also use this same suppressor on a HK USP 9 and a Beretta M9 with the same set-up (just switching the spring for the spacer). They are both pretty consistent with POI when switching between suppressed and unsuppressed.

    If it was blow-by causing the issue, wouldn't it present itself with the pistols also?

    Kurt, I appreciate the feedback. I think I will try that tomorrow and see if I have any luck.

    If not, I will just buy another barrel with 1/2 x 36 threads and another piston to see what happens. I think I would like a little longer barrel anyway. Boy this hobby is addictive and expensive.
     

    rcm192

    Sic semper tyrannis
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    May 31, 2010
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    If you do not have baffle strike, and im think you dont, because you didnt mention the suppressors exit hole, being out of round, you are experiencing a high amount of blowby in the last baffle or 2. Blowby is the hot gas that beats the bullet through the hole. Too much will cause a shift. Contact the manufacturer

    If its bad enough they may replace it.
     

    Rainsdrops

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    imagine your bullet traveling through the baffles, in your suppressor, behind it, is hot burning gas. some of that gas moves ahead of the bullet, as it passes through the hole. this is called blowby. suppressor manufacturers minimize blowby, by keeping the baffle's hole diameter, very close to the diameter of your bullet. an 9mm (.355 caliber) may have a (.410) diameter baffle hole.

    If the baffle hole, is overly large, the gases that get ahead of the bullet, can cause a shift in the bullets point of impact.

    Baffle hole diameter, isnt the most critical part of suppressor design. i suppressor, with a signifigant amount of blowby, can still effective reduce sound, and muzzle flash. Accuracy will suffer though.

    I'm just throwing blowby out there as a possibility. If you have time, and don't mind, could you take pictures, of your suppressor end caps, and post them here.

    anyway the bullet spins, I would email the manufacturer. Let them know you put the weapon in a shooting vise fired 3 shots unsuppressed and measured the distance, from point of aim and the holes on target. (and distance between holes)
    Next you attached your suppressor, without removing the firearm from the vice, and fired 3 shots suppressed and performed the same measuring procedure.

    your pics and test results, will give them an idea, of what going on.

    You may get lucky and they swap out your internals
     

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