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?

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.

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.

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.

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?

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?

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.

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

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.

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