Is BCG bottoming out?

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  • Is BCG bottoming out?

    New to the forum, AR's, and to reloading. Read some where that was a crazy thing to do, but I'm having fun. I've got a 24" 264 LBC super varmint. I loaded some 120 balistic tips with 2520 the groups were ok, maybe changing COL would help me. At29.9 gr up to 30.6 gr (the top load listed on the AA load data) the action seemed to work a lot harder, cases were landing 6 - 10 ft between 3 and 5, so straight out to slightly back. Primers looked ok, no Case head swipe (brass extrusion), but I couldn't tell if the bolt carrier was bottoming out or hammering the action.

    Are there any tell tale signs if the bolt carrier is bottoming out?

    I'm going to buy some more factory AA ammo and try to figure out how to set up my cronograph to check velocities of factory vs handloads. Going to practice with the crono using an air rifle at home so I don't waste alot of ammo. Annoying thing is most of the lights in my basement are flourescent so I have to set up some incandescents and turn the other off.

    Reply from LRRPF52:
    What buffer are you using? You'll have a lot more dwell time with that 24", and 120's over 28.5gr of 2520 will feel somewhat hefty if you have a standard carbine buffer. I'm not sure what buffer/recoil spring/bolt carrier weights you have. They should be on the heavier side with the Grendel, especially with 120+ gr bullets and stiff loads.

    The super varmint comes with a standard A2 stock with rifle buffer and spring. I did cursory search and I thought rifle buffers only came in one weight. I could try a stiffer spring I guess. It may take me a month or more to find the time to figure out the crono and then start low and work my way up again checking velocities. I would rather not blow a primer or damage the rifle or myself.
  • mtn_shooter

    #2
    In extreme cases, there will be a square indentation on the upper part of the buffer tube opening from the bolt carrier key hitting it. The buffer should, however, be long enough to prevent that, so that only the rubber/plastic part of the buffer hits anything.

    Comment


    • #3
      As long as the correct buffer AND recoil spring is used in the extension tube you have, I can't see this happening. The buffer pad will touch the rear inside of the receiver extension, or the spring coils will collapse totally against each other. If you put a carbine buffer in a rifle extension, I could foresee some problems. Also, at what point will the rear of the carrier key impact the charge handle, versus the base of the carrier key hitting the receiver extension. This shouldn't be happening either way.

      Comment


      • #4
        I just went and checked this on one of my AR's-a rifle-length extension tube with appropriate buffer and recoil spring. The buffer impact pad bottoms out before the carrier key gets anywhere near impacting the extension tube.

        Comment

        • RangerRick

          #5
          A lot of Grendels seem to be overgassed. I took the advice of folks on here and installed an adjustable gas block. I adjusted it to easily eject all my loads. Now my brass is cleaner and not as beat up.

          Rick

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          • bwaites
            Moderator
            • Mar 2011
            • 4445

            #6
            Originally posted by RangerRick View Post
            A lot of Grendels seem to be overgassed. I took the advice of folks on here and installed an adjustable gas block. I adjusted it to easily eject all my loads. Now my brass is cleaner and not as beat up.

            Rick
            When the ammo runs a gamut where the top factory load is almost 50% heavier than the lightest factory load, overgassing just about has to be standard, to make sure the rifles run with the 85-90 grain loads and the 130 grains loads.

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            • #7
              Originally posted by bwaites View Post
              When the ammo runs a gamut where the top factory load is almost 50% heavier than the lightest factory load, overgassing just about has to be standard, to make sure the rifles run with the 85-90 grain loads and the 130 grains loads.
              Yup. You have to "over-gas" a self-loader not just to swallow a wide diet, but to work even with a limited ammunition selection across different temperature and climate conditions. A gun runs much better in the summer than in the winter...

              Comment


              • #8
                Good info all around, I like the adjustable gas block to handle all the different ammo types, and I believe this will help with the dwell time after the bullet passes the gas port to make it out of the 24" tube, especially with the heavier bullets.

                thanks
                Sligo

                Comment


                • #9
                  You can also check Slash's Heavy Buffers online. Slash builds nice buffers and they do exactly what your looking to fix. Had same issue with .308 AR especially with suppressor. Adjustable gas block helped but new heavy buffer and spring fixed it.

                  Comment

                  • jwilson1985

                    #10
                    get tungsten powder online 15-20$ to but in your buffer and a wulf spring.. play with the powder weight till its how you want it in your buffer

                    Comment


                    • #11
                      Originally posted by jwilson1985 View Post
                      get tungsten powder online 15-20$ to but in your buffer and a wulf spring.. play with the powder weight till its how you want it in your buffer
                      You can find this yourself online, but just a note to consider. Powdered Tungsten, though pretty cool stuff to work with, is around half the weight of solid tungsten for the same occupied space. As a matter of personal experience, cast lead is slightly heavier for the same unit volume and a lot less expensive. It's quite easy to scrounge up a piece of EMT or other tubing (not copper), pinch an end shut in a vise, melt some lead and cast a dowel that fits in your buffer body. Replacing the sintered iron or whatever the standard weights are made from, weights in your buffer with a cast lead dowel will increase the weight somewhere between 30 to 40%. That can do wonders for taming an over-gassed setup.

                      Hoot

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