ar-15 short stroking

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  • bigtattoo79

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    M&P Sport 2 with 500rds down the pipe and never a malfunction. A couple weeks ago I hit the range and it started short stroking. I've changed ammo, mags and cleaned it nothing helps it either won't pick up the next round OR I get a bolt over base malfunction.

    Any ideas on what I should try next.
     

    shrxfn

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    Oct 25, 2015
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    Only thing left would be gas block, tube and gas port. Make sure nothing is obstructing them and also make sure the gas block didn't move. I had that happen once rifle worked fine then suddenly stopped cycling right. Turns out gas block had moved a little bit obstructing the port. Contacted manufacturer they told me that on their barrel it should be about a dollar bills thickness off the shoulder where the gas block sits. Checked and it had a larger gap so I moved it back and it started functioning fine again. Not sure if that is for all manufacturers or not.
     

    homeslice

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    If you search here you'll see the problem I was having with a DPMS for a family member. After some rapid firing the roll pin that was holding in the gas tube at the block had fallen out. May be worth checking. You can also look for gas leaks around where the tube goes into the block. Here's the thread I mentioned above: https://www.bayoushooter.com/forums...S-AR15-Ejecting-but-not-picking-up-next-round

    Good luck sir!
     

    jdindadell

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    Likely a gas issue, my check for that is to put some tape around the flash hider to cover the side ports but leave the muzzle open. Remove the bcg and the lower. Put your pinky (or any finger that will fit) into the camber and plug the breech end of the barrel. You could also use something like a foamy ear plug or anything that can be used to temporarily seal the chamber. Now heres the part you want to do alone, in case anyone tries to take a picture and put it up on dem internets... Put your mouth on the tape and blow (keeping in mind I am not your uncle). You should be able to hear and feel the air coming out of the gas tube where it ends in the upper receiver. Or you can use some sort of low pressure air supply (Like I do) to force air down the barrel. Probably a better idea than using your mouth, but when in Rome!!!

    This technique is easier than disassembly, and will easily determine if there is a blockage. Partial blockage can be more difficult to diagnose, does this gun have a pinned, or set screw gas block?

    I would also remove the buffer and spring and inspect those parts and the buffer tube for any damage, wear, or foreign objects.

    I am assuming you have cleaned and checked the bcg. Make sure the ejector roll pin is flush or below flush in the bolt body as that can cause dragging and sluggish function.
     

    bigtattoo79

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    Likely a gas issue, my check for that is to put some tape around the flash hider to cover the side ports but leave the muzzle open. Remove the bcg and the lower. Put your pinky (or any finger that will fit) into the camber and plug the breech end of the barrel. You could also use something like a foamy ear plug or anything that can be used to temporarily seal the chamber. Now heres the part you want to do alone, in case anyone tries to take a picture and put it up on dem internets... Put your mouth on the tape and blow (keeping in mind I am not your uncle). You should be able to hear and feel the air coming out of the gas tube where it ends in the upper receiver. Or you can use some sort of low pressure air supply (Like I do) to force air down the barrel. Probably a better idea than using your mouth, but when in Rome!!!

    This technique is easier than disassembly, and will easily determine if there is a blockage. Partial blockage can be more difficult to diagnose, does this gun have a pinned, or set screw gas block?

    I would also remove the buffer and spring and inspect those parts and the buffer tube for any damage, wear, or foreign objects.

    I am assuming you have cleaned and checked the bcg. Make sure the ejector roll pin is flush or below flush in the bolt body as that can cause dragging and sluggish function.

    I've cleaned and inspected everything.
    I've blown compressed air though the gas tube.
    Pinned gas block.
     

    rcm192

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    Make sure your gas key on top of you bolt carrier hasnt come loose. If it doesnt make a good seal around the tube you could have a leak there.
     

    shrxfn

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    Check the gas rings and make sure the gaps are not aligned or the rings aren't bad.

    Have you checked to see if it will hold open on an empty mag?

    Is it ejecting the brass? If so what O'clock is it at?
     

    bigtattoo79

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    Checked your buffer tube? Cleaned and greased properly?
    Buffer tube cleaned. Buffer and Buffer Spring cleaned and got a lite coat of oil on them.

    Check the gas rings and make sure the gaps are not aligned or the rings aren't bad.

    Have you checked to see if it will hold open on an empty mag?

    Is it ejecting the brass? If so what O'clock is it at?
    Gas rings look good and gaps are set in the proper location.

    Will not lock back on last round.

    I'd say right at 3 O'clock.
     

    jdindadell

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    I would remove the gas tube and inspect for a partial clog. Same with the gas block... Not so easy to remove the gas block since it is pinned. Inspect the pics and one side will have a smaller diameter than the other. Punch them out on the small side.

    Have you ever run 22lr thru it?
     

    bigtattoo79

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    I would remove the gas tube and inspect for a partial clog. Same with the gas block... Not so easy to remove the gas block since it is pinned. Inspect the pics and one side will have a smaller diameter than the other. Punch them out on the small side.

    Have you ever run 22lr thru it?

    I have the punches made for those pins and have removed gas systems in the past so no biggie there.

    It's never had .22 though it.

    - - - Updated - - -

    I had this exact condition and it was caused by the gas key set screws on the BCG coming loose. Blue loctite fixed it for me.

    I've checked it and all is tight.
     

    cajun 22

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    Check the gas rings on your bolt by taking the bolt and carrier out of the gun, extend the bolt forward and stand the carrier on the bolt, if the carrier comes down on the bolt rings are shot. If the carrier stays up, rings are good.
     

    bigtattoo79

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    Check the gas rings on your bolt by taking the bolt and carrier out of the gun, extend the bolt forward and stand the carrier on the bolt, if the carrier comes down on the bolt rings are shot. If the carrier stays up, rings are good.

    That's a cool trick to check it thanks for the tip.


    BTW: It passed this test.
     

    shrxfn

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    The weird thing is that according to the diagram 3 O'clock ejection means it is gassed correctly.

    Have you tried this upper on a known good lower that uses an upper with the same length gas system?
     

    bigtattoo79

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    Got a different buffer you can swap it out with?

    The weird thing is that according to the diagram 3 O'clock ejection means it is gassed correctly.

    Have you tried this upper on a known good lower that uses an upper with the same length gas system?

    My other ARs are mid length gas systems. My brother just said I can borrow one of his carbine gas ARs this weekend to swap parts around.
     

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