suppressor use and POI shift

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  • dammitman
    Warrior
    • Dec 2012
    • 647

    suppressor use and POI shift

    so with anyones actual experience what do you think is the main contributing factors to the point of impact shift when using a suppressor? I have been contemplating the purchace of a unit for specifically 6.5 use but like to do research before such a deal and I have done form 1 suppressor and am considering that route as well. I have read a lot from the super smart folks on some sites and they all seem to have the answer but like to accumulate all info possible. I really think it has all to do with the harmonics of attaching a pound of weight to the end of a barrel and its really a tiny few who doing such has no effect on POI. what do you think?
  • Klem
    Chieftain
    • Aug 2013
    • 3507

    #2
    Correct, although I suspect it has less to do with harmonics and more to do with the weight changing the way the gun recoils while the bullet is still in the barrel. Plus you get a few more fps due to freebore boost. While the suppressor is not as efficient as a barrel in containing pressure it does give you up to 10fps more. This, plus the weight on the end of the barrel is what changes your POI.

    The few with no difference between shooting on and off is indeed rare - I have never seen it. A difference of about 1Mil/3MOA is normal.

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    • dammitman
      Warrior
      • Dec 2012
      • 647

      #3
      thanks klem, your a pretty smart guy. I watched those videos about barrel harmonics and it made me think but sometimes I overthink stuff for sure. I am really tired of waiting for the hearing protection act to never happen so I am gonna apply for some form ones and make shooting great again. probably just build and leave on the guns.

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      • VASCAR2
        Chieftain
        • Mar 2011
        • 6219

        #4
        I don’t own suppressors because I live in Illinois but I’ve read where a 30 caliber suppressor is desireable for the 6.5 Grendel. Maybe versatility because you could use a suppressor for .264/6.5, .270/6.8 plus 7.62/30 caliber. Not sure but 30 caliber might also have less back pressure on a gas gun (direct impingement or gas piston) like the AR-15.

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        • dammitman
          Warrior
          • Dec 2012
          • 647

          #5
          I purchaced a 762-SDN-6 AAC quick detach suppressor a couple years ago and have several of the barrel adapters on several rifles. they make one using 9/16x24 threads so of course I have it on a AA barrel. works fine but I am wanting to dedicate units for all. really thought that the hearing protection act was gonna happen to make everything go quicker but its lookin like that's not gonna happen. the AAC took 9 months to be approved but again that was 2 years ago. I have heard its goin faster now.

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          • LRRPF52
            Super Moderator
            • Sep 2014
            • 8569

            #6
            Lack of concentricity and square shoulders, threads, and the mating surfaces will also contribute to POI shift.
            NRA Basic, Pistol, Rifle, Shotgun, RSO

            CCW, CQM, DM, Long Range Rifle Instructor

            6.5 Grendel Reloading Handbooks & chamber brushes can be found here:

            www.AR15buildbox.com

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            • SDet
              Bloodstained
              • Sep 2016
              • 82

              #7
              So, you've got a few things going on with poi shift. Simplest to see is the weight. This will effect harmonics to some unpredictable degree, less with a heavier barrel. It will also cause the barrel to flex, no different than resting the barrel on a barrier and seeing a shift, also less with a heavier barrel.

              These are relatively small changes and extremely repeatable.

              The other effect is bore concentricity (possibly spelled wrong), this has 3 factors, how parallel the bore of the barrel is to the can, how shifted, off center, the suppressor bore is from the barrel bore, and how straight the bore of the suppressor is (just like a barrel, there'll be a slight curve).

              All three of these will effect the bullet in the same way, if the bullet passes too close to the bore of a baffle or the exit end, the high pressure area around the bullet will deflect it. You don't have to have a strike to send a bullet keyholing or way off course. Just like a passing truck will move your car, the bullet will feel that same force as it passes through each bore.

              The tricky bit about this issue (since it's normally greater) is that it can be affected by many parts, so it can be very unrepeatable. If the suppressor doesn't index the same every time, if it is able to wiggle on the mount (we're looking at thousandths of an inch), or if things move with heat, you will see large poi shift. An oversized bore can help compensate at the cost of effectiveness.

              Pretty much, heavy barrel, light suppressor, and keep everything straight, and you'll minimize poi shift. But repeatability is the more important factor.

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