7.62x39 Ar pistol issues

Discussion in 'AR-15 Discussion' started by Tealduck0516, Apr 15, 2018.

  1. Tealduck0516

    Tealduck0516 New Member

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    I have built an AR pistol in 7.62x39. I have a problem with the gun feeding and locking back on an empty magazine. I have tried 3 different magazines, 2 bolt carriers, 3 different weight buffers, and numerous types of ammo all with the same results. Gas block is alignment has been checked, the gas port is centered in the carbon ring that has built up. Am i correct in assuming its under gassed? Thanks in advance. Pictures attached showing how the bolt locks on empty mag after one round vs pulling charging handel.

    Thanks

     
  2. Sgt_Skrb_25

    Sgt_Skrb_25 Well-Known Member

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    What length is the barrel? (7.5”, 10” ...ect) Are you running a standard pistol length gas tube, carbine? This will help in figuring out if there is under gassing issues . What brand mags have you tried ?
     

  3. Greg_r

    Greg_r Well-Known Member

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    I built a 7.62x39 just for the challenge. I knew about the supposed issues, and sure enough, I had them. Same-same as you.

    Two things fixed it and it ran almost 100%.

    First, enlarged the gas port. Just a little at a time. It's easy to remove but hard to put back.

    Second, machine the feed ramp from A4 style to a single large ramp.
     
  4. Tealduck0516

    Tealduck0516 New Member

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    7.5 inch barrel with pistol gas tube. I have tried 2 different asc 20 rounders, 1 asc 30 round and 1 c products 10 round. All same results. I have fixed the feed ramp issue and it cycles perfectly by manual operation. I have debated making the gas port bigger and going to an adjustable gas block to dial it back if needed.
     
    towboater likes this.
  5. Sgt_Skrb_25

    Sgt_Skrb_25 Well-Known Member

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    I know you said you tried different buffers. I think I’m running an H3 in mine. Did you try H3 or heavier?
     
  6. Sgt_Skrb_25

    Sgt_Skrb_25 Well-Known Member

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    7.62 is a higher pressure round it should be giving you plenty of gas. Not sure that drilling out the gas port is the fix. I’m thinking you might need more dwell time on your gas. Have you seen the Phase 5 pistol gas tube? It took me a while to balance my 7.5” pistol, buts a 5.56. I do have a 7.62x39 16” build hat works flawlessly. When you do fire , where is the round ejecting? I ask because maybe it’s over gassed. ? IMG_6081.jpg


    IMG_6080.jpg
     
  7. Tealduck0516

    Tealduck0516 New Member

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    Haven’t had time to get out and shoot it to check ejection angle. Thanks everyone for all of the help.
     
  8. Artie1957

    Artie1957 Member

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    Check to make sure that the gas key is bolted tight to the BCG and that the bolts are properly staked.
     
    Sniper03 likes this.
  9. fsted2a

    fsted2a Well-Known Member

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    Have you fixed the problem? Just curious to know? If not, you may want to consider the magazine.
     
    Brian138 likes this.
  10. Mikeb420

    Mikeb420 New Member

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    I'm new to AR platform but 90 % of feed issues is fixed with grinding down the center of the a4 type dual feed ramps into one wide large ramp... This is due to the high amount of taper in the casing compared to the almost straight wall of the 223 5.56 casings and bit due to the ratio of the taper over the given length of the cartridge when the rim of the rear leaves the feed lip at a specific point in geometry.

    As far as locks back.. Check that the Mag is making good contact to the lever.... And while I have no experience personal to the under gassed issue.... I've heard MANY people enlarge the barrel gas tap hole... I think one person said 1/8 inch is what the ran....

    In theory... In my opinion... I would use an adjustable gas block first... The if you over gassed it by drilling the barrel... At least you're able to tune it down if it's tooooo much...
    Like I said I'm new to ar15 in particular... But I've built at least 20 ak47s...and have smithed probably 200 guns in total.... I'm no pro... But I know alot