zero change with suppressor

[Squatums]

Hello All
Large zero change between suppressor installed and removed,
I have a AR pistol, Aero Precision upper in .300 Black Out, 8 1/2 inch barrel, not sure of twist, believe 1:8. Flash suppressor is Dead Air quick attach and suppressor is Dead Air Sandman .30 caliber.
Zero at 25 yards ( as this will be home defense weapon ) with no suppressor.
Ammo is Remington 220 gr subsonic open tip
Throw on suppressor and consistently pulling left 4 to 5 inch and 2 to 3 inch low.
Shot groups remain good, perhaps a bit open with suppressor.
Is this to be expected?
I guess I can re-zero with suppressor on since that would be the normal usage.

Also I did put that same suppressor on my LWRC Repr AR10 and noted groups all over the place. ( maybe ammo issue... this AR10 seems to prefer 168gr and i was using 147 gr 7.62.) or simply difference was shooting 100yds AR10 vs 25 yds AR15.
I did not put time/money into resolving that yet.

 

[LocoGringo]

It is normal to have an impact shift by adding a suppressor. I don't know the specs on the Dead Air suppressor, but anytime you hang a big weight off the end of your barrel, it's going to change the barrel harmonics. A suppressor "shouldn't" change a group size, but I suppose it's possible. One thing to check and be sure of is that you haven't gotten a baffle strike and that the suppressor is attached tightly. I had a waterfall effect on my target when my suppressor was just a hair "off" and the bullets were skipping off the endcap.

The best thing you can do in my opinion, of course, is zero the firearm as you intend to use it (with suppressor or without), find ammo that gives groups that you're satisfied with so that the entire package is ready for use, and then start experimenting with POI shift, group size, etc.

You also don't explain your testing technique. Are you resting the gun on something, shooting offhand, somewhere in between? What kind of sights are you using? Lacking a lot of info.

 

[Squatums]

It is normal to have an impact shift by adding a suppressor. I don't know the specs on the Dead Air suppressor, but anytime you hang a big weight off the end of your barrel, it's going to change the barrel harmonics. A suppressor "shouldn't" change a group size, but I suppose it's possible. One thing to check and be sure of is that you haven't gotten a baffle strike and that the suppressor is attached tightly. I had a waterfall effect on my target when my suppressor was just a hair "off" and the bullets were skipping off the endcap.

The best thing you can do in my opinion, of course, is zero the firearm as you intend to use it (with suppressor or without), find ammo that gives groups that you're satisfied with so that the entire package is ready for use, and then start experimenting with POI shift, group size, etc.

You also don't explain your testing technique. Are you resting the gun on something, shooting offhand, somewhere in between? What kind of sights are you using? Lacking a lot of info.

Thank you for response.
I actually started this by wanting to test what powder load works best for this gun with my reloads.
Reloads are what I expect for my home defense Hornady Sub x 190g and trying Hodgdon CFE/black for powder. 11g, 11.5g & 12g to start.
Concern about possible baffle strike if round not stabilized is what led me to start with suppressor removed.
Shot the factory loads mentioned in my post to zero at 25 yards, then rechecked with suppressor on and discovered the POI shift.
Using Holosun red dot sight and shooting at bench with sandbag support.
So, I guess just checking if POI shift is normal, can vs no can, and if so is 4 to 5 inch left & 2 inch low normal at such short range? 25 yard.

 

[LocoGringo]

I have no idea about what a "normal" POI shift would be. Some cans claim zero POI shift, but that must be tested and confirmed. I would be very surprised at a 4"-5" POI shift at 25 yards. That seems like a lot. The best thing I can think of is do your homework and find out what the twist rate in the barrel is and the maximum grain bullet that twist rate is capable of stabilizing. Without really knowing, I would guess baffle strikes. Is the bullet keyholing in the target?

 

[mcb]

There is typically a point of impact move between suppressor on and off. The amount your POI is moving on you 300 BO is more than I have seen typically. My point of impact change with my 300 BO pistol at 25 yards is hard to even notice. Usually it's on the order of 1-2 MOA with most of the guns I have used in both configurations.

Make sure your mount is tight and that you suppressor on the mount is also tight with no play. A loose suppressor, even just a little loose, does weird things to accuracy and POI.

Adding the weight of the suppressor also effects barrel harmonics. This can be either good or bad. Sometime you find that a particular ammo/gun will shoot tighter groups with addition of the suppressor sometime it causes groups to open up. Which way it goes is much harder to predict and you basically have to test/tune your ammo for you setup.

 

[12Bravo20]

The change in POI has been well explained by everyone. One other thing to take into consideration is if the barrel threads are 100% concentric with the bore of the rifle and that the shoulder is square to the bore. Both can effect POI with a suppressor and even the POI of a muzzle brake. Definitely look for any baffle strikes like already suggested. I would also try different ammo or powder charges if reloading.

 

[Glockula]

I have seen very little POI change between 2 rifles with my suppressor. Within 1.5 inches of the original POI. It has tightened groups for both my 300 BO and my .308win. Thats the reason I went with Griffin. Their claim is the taper mount helps with repeatable point of impact shift. Mine has held true to that.

 

[MySuomi]

I have a sandman L 30 caliber with the keymount muzzle brake. When I first installed it, I had a huge POI shift. It was a touch worse than your shift. After screwing around with it for a week, I realized that I was not tightening the suppressor fully onto the muzzle brake device. Once I tightened it up, I had almost no POI shift.

The other culprit could be an incorrectly installed muzzle brake attachment.

Hope you get resolution to your issue.