Severe POI change with suppressor

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duman444

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My brother bought a Galil .308 pistol, that he could keep in the Kawasaki Mule when driving around property for hunting. Nice and compact even with suppressor-should be death on hogs.

However, he has not been able to get the gun on paper at 100 yds with suppressor. He has both a Thunder Beast Ultra 7 and another manufacturer and shooting at 100 yds, the gun is about 16" low with 150, 18" with 168 and 19" with 180 gr bullets. Stays consistent with either suppressor. Sans suppressor its grouping 3.5" pattern at 2" high at 100 yds.

My suppressor on both my AR and bolt action .308 only change POI by 3-5".

This is a pistol barrel and only 12" long as opposed to 16+ on rifles.

Anyone have any ideas? He is trying to get in touch with Thunder Beast, their website shows minimum barrel length for .308 to be 14.5", but I don't know if that is for suppression noise level or ?.
 
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When I hang a can on my 20" AR (A4 model) It hits about 20 MOA low and likes a different brand of ammo than with out the can.

Ammo it likes with out can: 1/4 MOA @ 200 yards (1/2")

Ammo it likes with can: 2 MOA @ 200 yards (4")

Either way, vermin die!

Ivan
 
No surprise there.

When working up subsonic loads for a 30/06 many years ago, I ended up with a 24 MOA change at 100 yards from the 190 grain Sierra MK load used without the silencer.

Zero = 100 yards with the 190 grain MK at 2,600 fps
Subsonic without silencer = + 12 MOA
Subsonic with the silencer = + 12 MOA or 24 MOA total

The rifle was a sporter with a sporter weight barrel. Short, fat and stiff barrels will not suffer such big changes in zero.
 
Not subsonic loads

Scharfschuetzer said:
No surprise there.

When working up subsonic loads for a 30/06 many years ago, I ended up with a 24 MOA change at 100 yards from the 190 grain Sierra MK load used without the silencer.

Zero = 100 yards with the 190 grain MK at 2,600 fps
Subsonic without silencer = + 12 MOA
Subsonic with the silencer = + 12 MOA or 24 MOA total

The rifle was a sporter with a sporter weight barrel. Short, fat and stiff barrels will not suffer such big changes in zero.
Click to expand...

We have also experienced the large POI change for super to subsonic. However, all of the loads listed above are supersonic and as I said in first post, supersonic prints 3-5 high sans suppressor and right on with suppressor when I have it zeroed with suppressor at 100 yds.

Not trying to go totally noiseless, so staying with known supersonic loads. Quiets it down to level that you don't need hearing protection.

Have not seen this large change in POI in rifles-pistol length may be different beast.
 
My suppressed .300 BLK was shooting 22" low with subsonic 190gr bullets and 18" low with 130 gr at 1800 fps at 100 yards. I haven't been around too many rifles with suppressors but there is always a very definite shift in POI.
My buddy had to put a 20 MOA scope mount on his 20 MOA receiver 6.5 CM PRS rifle when he put a can on it. He wasn't surprised which tells me that that much shift isn't abnormal.
 
Adding weight on the end of the barrel changes the barrel "harmonics". Barrels vibrate, flex when fired and different weights hung on the barrel will change the vibrations and the bullet exits the barrel at a different spot in the movement and changes the POI. IIRC, I saw some ultra slow motion videos of a barrel firing and while slight, the vibration/flexing was noticeable...

Not a ballistician, just have done a lot of research, so my opinion is worth what you paid for it...:p
 
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18-20 minutes of change is too much for harmonic variation, especially on a 12" barrel (a 12" AR10 barrel should be pretty stiff). There's something else going on.

Have you checked carefully to ensure the cans are concentric to the barrel, and for baffle strikes? If the barrel threads were improperly machined, it's possible you're getting a very slight baffle strike that could account for the POI change.

That kind of POI change is extreme if the ammunition is consistent. I would talk with both the suppressor and rifle manufacturers.
 
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As Rodan stated there something wrong with the threads, and it is prob the threading on the barrel, to get that much change in POI. I have never seen that much change even with 300 BO subs. I will not put any of my cans on a AK since I do not trust the threads on the barrel. Check inside the can. Be Safe,
 
I had a 300 black out< AR pistol with 9.5" barrel. POA vs POI with subsonic ammo was 9" at just 25 yards. Using supersonic ammo resulted in the same difference. I additionaly could not find the right ammo (factory or home loaded) that would cycle the gun completely both surpressed and unsurpressed. After 8 or 9 months and well over a thousand rounds fired, I gave up and sold the gun and have plans to destroy the suppressor and get it off the books.
 
Update

Well, my brother talked with IWI, manufacturer of the Galil. Per IWI since its a piston driven AK, normal suppressors will always have the huge change in POI. They told him that verbally, but would not put it in an email.

His suppressor manufacturer also said piston driven guns react differently with cans.

Guess we have learned something.
 
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