Grendel suppressed - asking for opinions on exhibited bullet drop

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  • Nukfror
    Unwashed
    • Oct 2017
    • 3

    Grendel suppressed - asking for opinions on exhibited bullet drop

    Curious what folks opinions are on my Grendel bullet drop behavior now that I have it working suppressed. I just installed a Bootleg adjustable carrier yesterday which made my Grendel a suppressed sewing machine.

    I have a 20" barrel with a rifle length gas tube. I have a sneaky feeling the barrel gas port size was contributing to the overgassed issue (meaning it might be slightly bigger than it needs to be ... I think my are lengths somewhat match for a 20" barrel with what's indicated here, http://gunhub.com/ar15/50981-gas-port-hole-size.html, by TaylorWSO).

    Unsuppressed the casings flew out at about 1 to 1:30 or so.

    Suppressed they flew out at about 12:15 - right along the barrel ... WAAAYYY overgassed.

    My suppressor is an AAC 762-SDN-6.

    The rounds I'm using are Hornday 123gr SSTs (https://www.hornady.com/ammunition/r...-123-gr-sst#!/)

    With the Bootleg carrier on "S" (suppressed setting), the casing are flying out at about 2:30-3:00. Perfect ... no misfeeds, no stove pipes.

    What I'm hoping is opinions on the apparent bullet drop. My scope center is at 2.75" above bore center. At 100 yards, my scope was adjusted 13 clicks (or so) Up to get back on center. So that's 3.25 inches (or so) of drop .. wow. My 300 black suppressed drops 2" if I recall correctly (16" barrel).

    Is that 3.25" drop normal or expected ? Seems rather like ... a lot.

    Second question, does this mean my bullets have slowed down ... it would seem to mean that ?
    Last edited by Nukfror; 10-16-2017, 04:12 PM.
  • Double Naught Spy
    Chieftain
    • Sep 2013
    • 2560

    #2
    What I'm hoping is opinions on the apparent bullet drop. My scope center is at 2.75" above bore center. At 100 yards, my scope was adjusted 13 clicks (or so) Up to get back on center. So that's 3.25 inches (or so) of drop .. wow. My 300 black suppressed drops 2" if I recall correctly (16" barrel).

    Is that 3.25" drop normal or expected ? Seems rather like ... a lot.

    Second question, does this mean my bullets have slowed down ... it would seem to mean that ?
    I am afraid you may be perceiving things incorrectly.

    Your .300 BLK (assuming 125 gr. Hornady SST with BC of .305 and 2300 fps) will give you roughly 3.85" of drop at 100 yards when fired from a perfectly level barrel. To get 2" of drop from your .300 BLK 125 grain Hornady SST round, you would need a velocity of roughly 3200 fps, so a bit basically faster than your average .308 firing 125 gr. bullets (~3100 fps). A Lehigh Defense 78 gr. CQ @ 2800 fps still gives you nearly 2.7" of drop at 100 yards.

    Your Grendel (assuming 123 gr. Hornady SST with BC of .51 and 2500 fps) will give you roughly 3.1" of drop at 100 yards when fired from a perfectly level barrel. To get 3.25" of drop, the velocity of your barrel would be ~2465 fps and that would assuming you were shooting a perfectly level barrel, not just approximately level, but perfectly level barrel.

    These are calculations from a ballistic calculator that assumes zero incline (level), scope and bore axis being at the same level, no crosswind, 65 degrees F, and plugging in the BC, weight, and velocity.

    You have made some mistake in your assessment somewhere. Your .300 BLK is not going to have less drop when firing a comparable weight round.
    Kill a hog. Save the planet.
    My videos - https://www.youtube.com/user/HornHillRange

    Comment

    • Nukfror
      Unwashed
      • Oct 2017
      • 3

      #3
      Hey, thanks very much for the reply.

      I likely didn't type up my original question correctly. Too much information. Ignore my 300 blank comments. Let me make this real simple.

      I have my Grendel zeroed at 100 yards un-suppressed using the Hornady 123gr SSTs. When I suppress the Grendel using the same ammo, I have to adjust the scope 13 clicks (1/4" adjustments) *UP* to get it back on center ... so 3.25 inches up.

      My question is ... is the 3.25 inches of additional adjustment for suppression on a Grendel normal/reasonable ?

      Comment

      • explorecaves
        Warrior
        • Sep 2014
        • 284

        #4
        Have you checked to see if your can is concentric to the bore? Offset can would definitely explain the drop

        Comment

        • Dave_H
          Unwashed
          • Jun 2017
          • 24

          #5
          Installing my suppressor drops my POI one full MIL at 100 yards with Hornady Black ammo. This is with an 18" Lilja barrel and a Sandman-S. It's been consistent so far, but my shooting has been limited to 110 rounds and all with the Black ammo. I zeroed the rifle unsuppressed and set the zero stops on my scope. I have to dial the scope up when I put the can on. I'll try to update this thread when I switch ammo or get a little more time to verify that this remains repeatable.

          Comment

          • Double Naught Spy
            Chieftain
            • Sep 2013
            • 2560

            #6
            Originally posted by Nukfror View Post
            My question is ... is the 3.25 inches of additional adjustment for suppression on a Grendel normal/reasonable ?
            Ah! Okay, I follow now. The adjustment isn't from suppression but from barrel droop due to the additional weight of putting the suppressor on the end of your barrel.

            I have seen (at my range) the addition of a suppressor create over 7" of drop (and 3 laterally) and you can find some Youtube vids that will also show some larger drops. Generally, the thinner the barrel relative to length, the more that the barrel will droop with the addition of a given suppressor. Heavier suppressors will cause more droop than lighter suppressors.

            Whether or not you get barrel droop will depend on a variety of factors. I have seen Youtube vids where there is very little change in POI. I have seen some where there is considerable change in POI. Believe it or not, but several folks have posted vids documenting just how much change that does or does not occur with their various rifles.

            Note that if you add a suppressor wrap to retard the heat or otherwise protect you from the heat of the suppressor, that will put extra weight on the end of your barrel and can exacerbate the issue.
            Last edited by Double Naught Spy; 10-17-2017, 10:45 PM.
            Kill a hog. Save the planet.
            My videos - https://www.youtube.com/user/HornHillRange

            Comment

            • ricsmall
              Warrior
              • Sep 2014
              • 987

              #7
              DNS hit it dead on. Your just seeing a change in POI from the added weight of can. Your trajectory will remain much the same as unsupressed.

              Richard
              Member since 2011, data lost in last hack attack

              Comment

              • Klem
                Chieftain
                • Aug 2013
                • 3507

                #8
                +1

                It is normal that the POI shifts low when a suppressor is attached to a gun.

                I recall a .223 that shifted its POI 1Mil down and 1/4mil to the right when a suppressor was attached. As you know, one Mil subtends 3.6" at 100yds. I needed to adjust 3.6" up at 100yds to return the suppressed gun to its unsuppressed zero.

                The barrel flexes with the extra weight of a suppressor but it also changes how the gun recoils while the bullet is still inside the barrel. Unsurprising the POI will be low with a weight on the end of the barrel minimising barrel jump.

                Comment

                • Nukfror
                  Unwashed
                  • Oct 2017
                  • 3

                  #9
                  Thanks for all the replies !!

                  The explanation make a lot of sense. Funny enough a buddy of mine and I share that suppressor on a gun trust. He has an AR10 7-08 with a 20" length barrel. His correction for suppressed at 100 yards is basically the same as mine 12-13 clicks. Not knowing about barrel droop before this question was asked here, we were really scratching our heads trying to figure out how a 7-08 and a Grendel would have basically the same correction for what-we-incorrectly-assumed-was-suppression using those two rather different rounds !! Makes a lot of sense now.

                  Again, thanks for the explanation - everyday is a school day. I feel sssssoooo much better about my Grendel now
                  Last edited by Nukfror; 10-18-2017, 02:53 PM.

                  Comment

                  • ALshooter
                    Unwashed
                    • May 2017
                    • 12

                    #10
                    I would think that the poi shift is due to the design of the suppressor, specifically the type of clipping used on the baffles. IIRC, the 762-SDN uses single sided clips. This is proven to cause poi shift.

                    You can test if it is suppressor weight vs suppressor design by firing the rifle un-suppressed laying on it's side then suppressed laying on it's side. If the weight causes the issue, poi should change in a similar manner, vertically. I would bet you see the poi shift more horizontally, direction being dependent on which side of the rifle is down.

                    I could be wrong though.

                    Comment

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