Mag Feed Accuracy

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  • Kritter
    Unwashed
    • Mar 2014
    • 22

    Mag Feed Accuracy

    I have a AR built with a Lilja ar740 in a noveske receiver set w/maxim BCG
    The problem i have narrowed down is when i single feed the gun will shoot 1/2" and when it is magazine fed it shoots 1-1/2"-2" groups. I reload i use lapua and LBC brass using forster dies. best load is 28.5 xbr .010 jump with 123 amaxes (no crimp) lee crimp shot worse

    Any Ideas why it shoots that bad when fed through the magazine (ar-stoner)?

    i figured this out later because i was single feeding during load work-up
  • Vasux86
    Warrior
    • Apr 2015
    • 108

    #2
    Check your neck tension. I've known of folks having the same problem because the bullets were sliding forward when the rifle chambered from rounds from the magazine.

    You could check this measuring COAL before you put a round in the magazine, load it in the mag, let the slide come forward and chamber the round, and then remove the round and measure COAL again.

    Comment

    • Kritter
      Unwashed
      • Mar 2014
      • 22

      #3
      Originally posted by Vasux86 View Post
      Check your neck tension. I've known of folks having the same problem because the bullets were sliding forward when the rifle chambered from rounds from the magazine.

      You could check this measuring COAL before you put a round in the magazine, load it in the mag, let the slide come forward and chamber the round, and then remove the round and measure COAL again.
      I measured a piece of sized LBC brass and ID of neck is .264 I'm guessing too lose and i guess i would have to run bushing dies... anyone mess with a Forster sizer button to tighten them up?

      Comment

      • Kritter
        Unwashed
        • Mar 2014
        • 22

        #4
        Any recommended dies? i am used to my lee collet kneck sizer with my .308
        Would sanding my expander button on a drill help?

        Comment

        • LRRPF52
          Super Moderator
          • Sep 2014
          • 8569

          #5
          I'm leaning more to Natural Point of Aim disruption from the return to battery stroke of the action when the gun feeds normally.

          Are you bagging the position heavily, both front and rear?
          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

          Comment

          • NugginFutz
            Chieftain
            • Aug 2013
            • 2622

            #6
            It's fairly easy to check if neck tension is your issue. Measure COAL of a few test rounds. Load up normally and fire a round. Do NOT fire the next round, but extract and remeasure. If the COAL has changed (+ or -), you have your answer.

            If you find that neck tension is an issue, either reduce the sizer ball diameter or you can pick up a Lee FCD. With the FCD you can increase the crimp until setback or sliding is eliminated.

            Several members can also tell you that using Redding bushing dies can also do the same without a sizing ball.

            Good luck on ID'ing your issue.
            If it's true that we are here to help others, then what exactly are the others here for?

            Comment

            • Vasux86
              Warrior
              • Apr 2015
              • 108

              #7
              Originally posted by Kritter View Post
              Any recommended dies? i am used to my lee collet kneck sizer with my .308
              Would sanding my expander button on a drill help?
              What is the OD of the expander button? This probably isn't the issue but you can easily measure to see if the expander button is limiting resizing or the issue might be found elsewhere.

              Comment

              • sneaky one
                Chieftain
                • Mar 2011
                • 3077

                #8
                Yes , kritter we have. On the Forster button- easy to fix , here and upon most. Hone it down a bit- take good measurements as you go- don't go past .260-.259.
                Last edited by sneaky one; 12-01-2015, 01:46 AM.

                Comment

                • Kritter
                  Unwashed
                  • Mar 2014
                  • 22

                  #9
                  Originally posted by LRRPF52 View Post
                  I'm leaning more to Natural Point of Aim disruption from the return to battery stroke of the action when the gun feeds normally.

                  Are you bagging the position heavily, both front and rear?
                  i normally shoot prone off a harris bipod and rear bag (load work up) but have tried it off a lead sled with same results
                  Last edited by Kritter; 12-01-2015, 02:57 PM.

                  Comment

                  • Kritter
                    Unwashed
                    • Mar 2014
                    • 22

                    #10
                    Thanks all I will try to do the coal test. I have a lee crimp die but didnt seem to help groups but have never checked for COAL change, I will try again. My Expander ball measures .264 i sanded it down to .263 before i read this. I think Neck tention may be why i was getting better groups with virgin brass?

                    Comment

                    • NugginFutz
                      Chieftain
                      • Aug 2013
                      • 2622

                      #11
                      Originally posted by Kritter View Post
                      Thanks all I will try to do the coal test. I have a lee crimp die but didnt seem to help groups but have never checked for COAL change, I will try again. My Expander ball measures .264 i sanded it down to .263 before i read this. I think Neck tention may be why i was getting better groups with virgin brass?
                      Did you develop your load using unfired new brass? If so, be aware that case volumes will be slightly different between new and fired brass. I'd done this, and saw a drop in velocity with the same load in the fired brass. A significant change in velocity can clearly have an effect on group sizes.
                      If it's true that we are here to help others, then what exactly are the others here for?

                      Comment

                      • Kritter
                        Unwashed
                        • Mar 2014
                        • 22

                        #12
                        Originally posted by NugginFutz View Post
                        Did you develop your load using unfired new brass? If so, be aware that case volumes will be slightly different between new and fired brass. I'd done this, and saw a drop in velocity with the same load in the fired brass. A significant change in velocity can clearly have an effect on group sizes.
                        My current load was tuned with once fired brass FL sized with shoulder bumped back a few thou. Using Forster datumdial. When I put cases in a case gauge they stick out a bit so I think my chamber a slightly big but passes go/no go test

                        Comment

                        • lwminton
                          Warrior
                          • Nov 2014
                          • 143

                          #13
                          Originally posted by NugginFutz View Post
                          It's fairly easy to check if neck tension is your issue. Measure COAL of a few test rounds. Load up normally and fire a round. Do NOT fire the next round, but extract and remeasure. If the COAL has changed (+ or -), you have your answer.

                          If you find that neck tension is an issue, either reduce the sizer ball diameter or you can pick up a Lee FCD. With the FCD you can increase the crimp until setback or sliding is eliminated.


                          Several members can also tell you that using Redding bushing dies can also do the same without a sizing ball.

                          Good luck on ID'ing your issue.

                          Does a magazine fed round enter the chamber in line with the bore? It looks to me eyeballing that it enters at a slight angle. If so I would think that could affect concentricity or grip. Just guessing.

                          Comment

                          • LRRPF52
                            Super Moderator
                            • Sep 2014
                            • 8569

                            #14
                            A cartridge enters the bore relatively centered, especially as it snaps into the bolt face recess.

                            It also has a lot of tension on it from the ejector and extractor, but gets aligned with the chamber. There isn't a lot of room to get off-center in there, unless the projectiles are experiencing runout from the press.

                            A way to avoid runout is to seat your bullets with two strokes, rotating 180 degrees after the first stroke. Large sample tests have been done with this method to demonstrate its effectiveness.
                            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

                            Comment

                            • lwminton
                              Warrior
                              • Nov 2014
                              • 143

                              #15
                              Originally posted by LRRPF52 View Post
                              A cartridge enters the bore relatively centered, especially as it snaps into the bolt face recess.

                              It also has a lot of tension on it from the ejector and extractor, but gets aligned with the chamber. There isn't a lot of room to get off-center in there, unless the projectiles are experiencing runout from the press.

                              A way to avoid runout is to seat your bullets with two strokes, rotating 180 degrees after the first stroke. Large sample tests have been done with this method to demonstrate its effectiveness.
                              I do the 180 twist but don't have a run out tool to check. There is a tool (Hornady?) to measure then correct run out-is it worthy?

                              What really happens when an M1 Garand fires the final round and the En-Bloc clip ejects with the distinctive Ping. Well thanks to the folks at ForgottenWeapons.com, you can see for yourself in super-slow-motion. The entire cycling process of a Garand has been captured using a high-speed camera running at 2000 frames per second (about sixty times normal rate).


                              Coincidently, I just watched this video of an M1 in slow motion. It shows the tilt of the bullet as it enters the chamber. It is hard to see if it completely straightens out before the lands but it looks like a close call. I guess I was thinking that the bullet grazing the top of the chamber is what oriented the bullet flat.
                              Last edited by lwminton; 12-04-2015, 08:29 PM.

                              Comment

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