Short Stroking? Or Something Else? Need The knowledge of the Forum.

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  • Bizzo24
    Unwashed
    • Jul 2017
    • 14

    Short Stroking? Or Something Else? Need The knowledge of the Forum.

    Happy Labor Day Everyone.

    I Built a new 6.5 Grendel and I'm having issues with it that I can't seem to resolve. I've read many of these forums surrounding the same issues but so far nothing is working for me. At least not to full resolution. I need your opinions on if something is getting hung up, vs timing issue, vs over/under gassed.

    First...let me give you parts list of the items that I think are involved with the issue:
    -18" JP Rifle Barrel Kit with Enhanced Bolt, and 2-piece adjustable gas block. RLGS
    -Battle Arms Development full Bolt Carrier with staked gas key.
    -BCM H1 Buffer
    -Tubbs Carbine Flatwire Buffer Spring.
    -Alexander Arms 6.5 Grendel Magazines.
    -and really reaching.....a Timney Trigger.
    * Using Factory Hornady 123 SSTs.

    After assembly, first trip to the range resulted in case ejection but no hold open. Started with GB 6 clicks open and worked my way out to full open.
    - For trouble shooting I installed empty magazines and pulled the charging handle.... bolt would lock open when manually done.

    After this first session, I broke the rifle down and rebuilt the upper. This time I was even more diligent to measure, mark, and align the gas port with the gas block....and assure the gas tube was perfect front to back. I also bedded the GB.

    Second range session. GB fully open, case ejection no hold open.
    Third Range Session:
    -- Replaced Tubbs Flat wire spring with standard carbine buffer spring. No change with most early settings of GB. Therefore....
    -- Replaced H1 Buffer with standard carbine buffer. Was able to get case ejection at 3:00 but not PROPER hold open.
    -- What I mean by proper is....As I opened the GB, eventually the Bolt Carrier would hold open, but not with the bolt catch....but rather on the lips of the magazine. See Pic. Yellow arrow. This occurred with all 3 magazines.
    -- Inspection of the brass showed 2 lines on the neck of the brass, and a corresponding flat spot in the same area. See pics.
    ---- However, I think the flat spot on the neck is coming from the brass hitting the brass deflector on the rifle. I got a glimpse of this on a slow motion video....and the flat spot got larger as I opened the gas block. See Green Arrow on Pic. of hit marks. But I still don't understand the lines on the brass. Is this normal?

    So, I have a gas block properly aligned, I'm getting gas through the system, the cases are ejecting but the bolt locks open on the lips of the magazine.

    Do these issues appear to be a gas problem, or hang up problem? In person, my gut says something is physically getting in the way.

    1) were the Tubbs Spring and H1 buffer to heavy for this system?
    2) was the Tubbs spring to long for the buffer tube. it had the proper coil number but it was substantially longer.
    - Again switching to standard carbine buffer and spring seemed to help.
    3) Bolt catch seems to be smooth with no resistance or grinding.....could it still be out of timing with the BCG?
    4) Is the BCG too Heavy? it's pretty robust and seems heavier than my DD and PSA bolt carriers. Should I be minimizing as much weight as possible in this area? I thought heavier would help with recoil.
    5) Could it be that JP Rifles drilled the gas port too small? They would not tell me proper size....said it was proprietary.
    6) Can the Timney Trigger's hammer be throwing the timing off by rubbing?
    -- Let me explain this. When you install the Timney there are two screws that you tighten to lock it against the trigger pins. In doing so the whole
    trigger assembly raises a bit.. is it possible this is causing interference? I'm reaching I know....but trying to look at everything.

    Looking at a slow motion video....I think the BCG is traveling all the way back and then coming forward and stopping on the lips of the mag. But I'm not 100% certain. If it's not traveling all the way back, then it's not enough gas, or too much weight, or something too long or binding....right?

    What steps would you take to resolve. Easiest to hardest.....cheapest to most expensive if possible. Already too much money in this thing. Need to get it running flawlessly.

    On a positive note......I was shooting 1" groups at 100 yards even though it looked like I had Parkinson's through the scope! This thing shoots better than I'm capable of right now.

    Appreciate the insight!
    Attached Files
  • Kilco
    Chieftain
    • Jan 2016
    • 1201

    #2
    I know that the lines on the neck and flat spot are perfectly normal. Just marks from the feed ramp and brass deflector. Both of my Grendels showed the same.

    Seems like you deff know your stuff, and there are many other that know far more than me on here. At first I was going to suggest trying another mag, but you said all three did the same thing..

    Does the rifle function fine besides the bolt not locking open? I mean will it cycle through a magazine without an issues? How does it cycle with the gas block turned down to more "normal" settings?

    I use a timney in my SR556 and a Velocity trigger in my R-15 30 RAR, both using the same set screw design as you mentioned and I don't believe that is causing you the issue.

    Have you tried a different buffer spring to eliminate that variable? Or tried a different BCG with your JP bolt to also eliminate that possibility? I'm intrigued as well... interested in what others have to say and hoping you keep us posted with this little "adventure"
    Last edited by Kilco; 09-02-2017, 09:42 PM.

    Comment

    • LRRPF52
      Super Moderator
      • Sep 2014
      • 8569

      #3
      Sounds like you're getting sluggish function.

      Also looks like you're getting short bolt hold open on carrier face, not the feed lips.

      Keep the carbine spring and buffer in there.

      Try changing these things one at a time:

      * BAD E carrier to standard bolt carrier, and polish the guide rails. (Are you lubricating with a thick, viscous oil BTW?)
      * Timney Trigger to LaRue MBT or Geissele

      That gun should be running well with the JP barrel and RLGS open, with a carbine buffer and carbine recoil spring.

      Another thing is that with many adjustable gas systems, they need to carbon-up before you start getting the correct amount of gas delivery back into the Stoner internal expansion system. I've seen some guns short in the beginning, then carbon-up the adj gas and run fine after that, but it sounds like something is wrong on the middle end, not so much on the front.

      I also bed my gas tubes to start with a clean slate for this reason, to eliminate that variable up there, and I also noticed that the LaRue Stealth 2.0 Grendel has a sealed gas tube with a press-fit bushing/ferrule to make this happen as well.
      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

      • bj139
        Chieftain
        • Mar 2017
        • 1968

        #4
        Are you using enough lube?

        Comment

        • Grendelshooter
          Warrior
          • Jun 2017
          • 214

          #5
          Not enough gas, maybe the gas port is too small?
          If it's short stroking with good ammo and standard BCG and recoil spring that's the first thing that comes to mind.

          My last 7.62x39 upper was doing the same thing. Standard carbine recoil spring, BCG, Geiselle trigger and mid length barrel with adjustable gas block. I opened it up with a 7/64 drill bit and reassembled. With the gas block fully open on that I got perfect function.

          Comment

          • Bizzo24
            Unwashed
            • Jul 2017
            • 14

            #6
            Kilco,

            I haven't tried loading the magazine up with rounds and trying to see what happens. I was so concerned with the short stroking that I didn't want to jam it with a live round. But it's worth a shot I think.

            Turning the gas block down yields less movement of the BCG and worsens the problem.

            I have tried different buffer from H1 to standard, and changed spring from Tubbs to standard. That did improve function....but did not solve.

            I have not tried a different BCG but that was next on my consideration list. I have a scale and want to measure the BAD Bolt carrier vs. my Daniel Defense bolt carrier to see if the weights are different. But right now I think the issue is in the middle.....not to trouble shoot what it is.

            Comment

            • Bizzo24
              Unwashed
              • Jul 2017
              • 14

              #7
              Originally posted by LRRPF52 View Post
              Sounds like you're getting sluggish function.

              Also looks like you're getting short bolt hold open on carrier face, not the feed lips.

              Keep the carbine spring and buffer in there.

              Try changing these things one at a time:

              * BAD E carrier to standard bolt carrier, and polish the guide rails. (Are you lubricating with a thick, viscous oil BTW?)
              * Timney Trigger to LaRue MBT or Geissele

              That gun should be running well with the JP barrel and RLGS open, with a carbine buffer and carbine recoil spring.

              Another thing is that with many adjustable gas systems, they need to carbon-up before you start getting the correct amount of gas delivery back into the Stoner internal expansion system. I've seen some guns short in the beginning, then carbon-up the adj gas and run fine after that, but it sounds like something is wrong on the middle end, not so much on the front.

              I also bed my gas tubes to start with a clean slate for this reason, to eliminate that variable up there, and I also noticed that the LaRue Stealth 2.0 Grendel has a sealed gas tube with a press-fit bushing/ferrule to make this happen as well.
              I agree. It definitely feels like sluggish function.

              Can you explain what you mean by "short bolt hold open on the carrier face"?

              I am using a thick grease....Slick 2000 EWL Grease on BC and Lube on the bolt. However, I don't generally over lube. Maybe I'll slap it on there for a bit to see if things loosen up.

              And I'll try my Daniel Defense BC or my Wife's PSA bolt carrier and see what happens.

              Thanks for the insight on the sealed gas tube.

              Comment

              • Bizzo24
                Unwashed
                • Jul 2017
                • 14

                #8
                Just compared the weights of my Daniel Defense Bolt Carrier and the Battle Arms Development Enhanced Bolt Carrier in my Grendel.
                To my surprise they are both the same at 9.4 oz.

                I think I'm still going to try a different carrier to see what happens. I'll keep you posted.
                Please let me know if you have any other ideas.

                Comment

                • grayfox
                  Chieftain
                  • Jan 2017
                  • 4295

                  #9
                  I'm with "sluggish" but there are couple of other things I'd suggest you can try. Both of my AR styles when new did this but smoothed out after 50 rounds:
                  1. thoroughly clean out the chamber. New ones many times have some grease or gunk or something in there that tend to slow down the cycling. I've even taken some fine fine polish compound onto a .410 cloth plug or silk cloth (NOT the brass bristle!!) and hand-twisted it in the chamber to polish it just a ***teeny*** bit.
                  2. Shoot about 50 rounds - I did 'em one at a time b/c of the same short stroking and weak ejections. After that everything loosened up and started working much better. So break-in may not be done for this new gun.
                  3. I run bolts and BCG's dry or almost dry - that's just me. I'm not in a humid or cold environment here in northern VA. When I hear the word "grease" it just sounds too thick for me, esp in new BCG's. But I will also clean newbies more often to keep out the carbon buildup.
                  4. If you have a nice NiB carrier try using that one... at this point slicker is definitely better.
                  5. When cleaning the bolt stand it on end and cycle the ejector plunger up/down several times (I use closed needle-nose pliers) to ensure no gunk or brass flakes are slowing down its springy-ness.

                  Anyway couple of thoughts that helped me with mine.
                  ps, I ended up with a JP centerless spring and Spikes heavy/KAW 4.3 to smooth things out a bit, but that was after ~400-500 rounds.
                  "Down the floor, out the door, Go Brandon Go!!!!!"

                  Comment

                  • Lastrites
                    Warrior
                    • Apr 2017
                    • 678

                    #10
                    The bolt face should be 1/8" to 1/4" in front of the rear edge of the ejection port when you manual pull the charging handle to the rear, would be something to check. Also check for the hammer binding on the bcg when you manually pull it back, if in the last couple of inches of the pull feels harder or has more resistance the hammer is binding on the bcg.

                    Comment

                    • grayfox
                      Chieftain
                      • Jan 2017
                      • 4295

                      #11
                      "Short stroking" is explained by a TTAG article from 2011, among other places...
                      “an attempt to cycle the action of a firearm (any firearm; rifle, pistol or shotgun) with a loaded magazine that fails complete the full mechanical cycle of the action, resulting in a failure to chamber the next round in the magazine and/or a failure to reset the fire control group, resulting in a failure to fire.”
                      The most popular and widely respected voice in America for your gun rights, breaking 2nd Amendment news, and everything else you need to know as a gun owner...
                      "Down the floor, out the door, Go Brandon Go!!!!!"

                      Comment

                      • Kilco
                        Chieftain
                        • Jan 2016
                        • 1201

                        #12
                        I'm just curious if it cycles ammo when firing and simply doesn't lock the bolt on last shot, or short strokes and either doesn't grab another round or binds up upon feeding..

                        This info would be useful to determine if it's either a gas issue or a mechanical issue.

                        Comment

                        • VASCAR2
                          Chieftain
                          • Mar 2011
                          • 6219

                          #13
                          Are you sure your buffer tube is a carbine length tube. Using a rifle length buffer tube with carbine spring and buffer could create issues. I'd also inspect the buffer tube to make sure it isn't bent or dented and affecting the buffer and springs movement.

                          Comment

                          • Kilco
                            Chieftain
                            • Jan 2016
                            • 1201

                            #14
                            Originally posted by VASCAR2 View Post
                            Are you sure your buffer tube is a carbine length tube. Using a rifle length buffer tube with carbine spring and buffer could create issues. I'd also inspect the buffer tube to make sure it isn't bent or dented and affecting the buffer and springs movement.
                            I was also wondering the same thing when he said both springs side by side one was noticeably longer than the other

                            Comment

                            • Lastrites
                              Warrior
                              • Apr 2017
                              • 678

                              #15
                              Originally posted by Kilco View Post
                              I was also wondering the same thing when he said both springs side by side one was noticeably longer than the other
                              The Tubbs flat wire spring is supposed to be longer that a regular std spring by 4 or more inches, that said it will collapse about 2 inches shorter when fully compressed, I doubt it's the Tubbs.

                              I would pressure test the battle arms bcg to check for leaks at the key. Need to have an air compressor, short tube to fit the key and stick an air gun to it, spray CLP around the base of the key and pressurize. If you see bubbling, you have a key leak.

                              Comment

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