POI shift with different can weights

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plodder
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POI shift with different can weights

Post by plodder » Sat Jan 24, 2015 10:32 am

I have noticed that when I hang my stainless Form1 can on the end of my 16" .223 the point of impact at 100yds is nearly 4" lower than when I use my aluminum Form1 can or store bought Specwar 556. Group sizes remain consistent and acceptable regardless of which of the 3 cans are used.

Does a few ounces (haven't weighed them yet) weight difference make for such a dramatic difference in point of impact at 100 yds or could it be something else?
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T-Rex
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Re: POI shift with different can weights

Post by T-Rex » Sat Jan 24, 2015 11:38 am

Im not going to go into cone clips or alignment, I'll just comment on weight.
With a heavier mass at the end of the bbl you're, in effect, suppressing muzzle rise = lower POI
The lighter suppressor does not have as much of an effect so the POI is higher.
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Re: POI shift with different can weights

Post by sub-sonic » Sat Jan 24, 2015 7:20 pm

could be barrel flex or you are supporting the gun behind the point of balance.
try shooting with the can on sandbags and see where the poi goes.
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Re: POI shift with different can weights

Post by Gunfixr » Tue Jan 27, 2015 12:01 pm

Simple barrel droop.
On a rather lightweight profile 14.5" pinned FH AR barrel, my almost 22oz. can drops POI almost 4".

The same can dropped POI about 2" on a Savage .308 24" heavy barrel tactical bolt rifle.
It was insanely quiet, almost "look down the bore to make sure the bullet left" quiet. I didn't like that much drop, and cut the barrel to 20". Same can now only moves POI 3/4".
Still plenty hearing safe, but I do miss how quiet it was.
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Re: POI shift with different can weights

Post by sizulku » Tue Jan 27, 2015 1:34 pm

If can weight that causing the POI shift, how to explain about AAC M4/SPR can that using AAC MITER mount have 5 adjustable POI positions?

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Re: POI shift with different can weights

Post by sizulku » Mon Feb 09, 2015 1:05 pm

sizulku wrote:If can weight that causing the POI shift, how to explain about AAC M4/SPR can that using AAC MITER mount have 5 adjustable POI positions?
any explanations?

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Re: POI shift with different can weights

Post by doubloon » Mon Feb 09, 2015 1:48 pm

It is more than just the simple weight of the can that contributes to POI. A rifle won't always shoot lower after a suppressor is attached. Sometimes it will shoot left or right or even high.

Regardless of the can weight barrel harmonics are going to play a significant role in POI shift between suppressed and unsuppressed. Barrel thickness, profile and length all play a role in harmonics.

Anything that touches your barrel has the potential to cause POI shift. If your barrel is properly free floated try this experiment. Shoot 5 shots at 100 yards, fold a dollar bill up and wedge it between your barrel and the stock then shoot 5 more shots.

Some video links

https://www.youtube.com/watch?v=_9ULBtsnkR0

https://www.youtube.com/watch?v=HDNrLGhyR_o

https://www.youtube.com/watch?v=L_E_GJayano

It is my understanding from a few old threads on the topic that baffle clearance will also affect POI, in some cases repeatably, which is why turning/clicking your suppressor to a different position will change downrange POI with no other adjustments to sights/ammo/etc. The reason for this IIRC is turbulence off the baffles "kicking" the bullet as it passes over/through baffle apertures. Expanding gas under pressure is a tremendously dynamic environment for physics.
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tf2addict
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Re: POI shift with different can weights

Post by tf2addict » Sat Jul 08, 2017 1:54 am

It's late and I'm tired but how do you put a folded up dollar bill between the barrel and stock??

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Re: POI shift with different can weights

Post by Fulmen » Sat Jul 08, 2017 5:03 am

doubloon wrote:Expanding gas under pressure is a tremendously dynamic environment for physics.
Well said. A silencer is a veritable treasure chest of extreme physics.

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Re: POI shift with different can weights

Post by doubloon » Sat Jul 08, 2017 5:06 am

tf2addict wrote:It's late and I'm tired but how do you put a folded up dollar bill between the barrel and stock??
like this only fold it so it fits snug
Image
http://www.youtube.com/watch?v=BDtd2jNIwAU MUSAFAR!
http://www.youtube.com/watch?v=8CrOL-ydFMI This is Water DavidW
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