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Thread: Semi auto 9mm ar15 pistol double tapping and stringing

  1. #1
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    Semi auto 9mm ar15 pistol double tapping and stringing

    i put together a 9mm pistol that has the adapter to use colt style mags. It has a aero 7.7oz buffer, standard spring. Some $90 bolt, 5.5" barrel, anderson lower, and some random upper i picked up a while back, am running a milspec trigger.
    So the thing will double tap, and sometimes do a string of 4 or so. I tested it with winchester 115gr, remington 115gr, and winchester 124gr nato.
    The winchester is the weakest, I normally just run it through my handguns as my Uzi doesnt like it. In this gun it cycles (albeit to well) for what its worth it throws the brass quite far in this gun. The remington normally runs good in all of my 9mms. The 124gr stuff is +p and runs great in everything.
    Did my testing this morning with it and those three ammunitions. I have heard that weak ammo can cause doubles, thats why i tried the 124gr. The last shot of 124gr fired partially out of battery. I think you can see some of the shell shards in the pictures.

    Any ideas on how to get this to operate properly?
    Attached Images      

  2. #2
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    Another picture
    Attached Images  

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    Decided to start swapping in different firing componants. Started with a different hammer, just did 25rds of remington without a hickup. Will post here if I have any further issues. The replacement hammer is from a different brand of parts kit. Had a anderson kit, this is some other brand I cant remember

  4. #4
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    Sometimes swapping Fire Control components can fix, or cause, problems.

  5. #5
    Registered User DINK's Avatar
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    Can we get a better look at the underside of the bolt? It looks like it might have been ramped a bit too much, in which case the hammer isn't getting cammed back far enough to reliably catch the sear. Swapping out the hammer might have cured this.

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    My limited experience with AR-15 doubling (regardless of caliber) has been resolved by adjustment (i.e. judicious filing/grinding) or replacement of the disconnector, disconnector spring, or the hammer.
    Best of luck.
    MHO, YMMV, etc. Be well. 2A

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    Here are some pictures as requested of the bolt.

    Will do some more shooting this weekend. Will post here if it has any further issues. Have to finish sighting it in.
    Attached Images    

  8. #8
    Registered User y2k87k2000's Avatar
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    A lighter buffer tube could help it as well

  9. #9
    Registered User DINK's Avatar
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    I guess I should have been clearer. The part of the bolt that is the area under consideration is the sloped part of the underside where the hammer is cammed back as the bolt is cycling. You will have to remove the bolt from the receiver and turn it over to get pictures of that.

  10. #10
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    I was told that doubling may be caused by a weak disconnector spring
    Any One Who Thinks The Pen is Mightier Than The Sword
    Obviously Never Encountered Automatic Weapons
    General Douglas MacArthur

  11. #11
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    I think that hammer took care of it. Did a 32 round mag without issue (would have definitely burped before).
    If I have any further issues will continue with the fire control group replacement as I seem to have enough lying around

    Heres a pic of the top of the bolt and the bolt face.
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