AR15 7.62x39 cycle issues

GMC Z · Nov 20, 2015

Built an AR chambered in 7.62x39. Test fired it for the first time today, fires one round, ejects the brass cleanly, but doesn't chamber the next round. I have a rifle length gas tube on a 20" barrel. Most forums I've read recommend opening up the gas port in the barrel, I've also read a couple that recommend changes in the weight of the buffer or springs. Leaning towards opening up the gas port, does anyone here have real world experience and recommendations? What size should the gas port be? Haven't taken any thorough measurements, but the round end of a 1/8" drill bit will not fit. Using an ASC 30 round magazine. Everything works when I cycle it manually.

erudne · Nov 20, 2015

1st disassemble and dry lube your mag, check mag catch to see if the catch is screwed even with the release button, check for burrs and dents in mag. Lube your recoil spring w/lithium grease. inspect your bolt and bolt locking recesses for burrs etc. Gas key correct? Is your ammo reloaded?
If the above are to spec try to locate an adjustable gas block and install.

Member 5605 · Nov 20, 2015

Verify your gas port is in the right spot on the gas block. It may go back far enough to eject but not to pick up another if they are misaligned.

Certaindeaf · Nov 20, 2015

One round? Probably all corroded.

Just kidding!

DRZ400S · Nov 20, 2015

Did you try just one round in the magazine? If it locks back gas port is fine.

GMC Z · Nov 21, 2015

DRZ400S said:
Did you try just one round in the magazine? If it locks back gas port is fine.

I'll give that a try.

GMC Z · Nov 21, 2015

Dyjital said:
Verify your gas port is in the right spot on the gas block. It may go back far enough to eject but not to pick up another if they are misaligned.

Checked it. Applied a little lock tight to the area to improve the seal, no change.

GMC Z · Nov 21, 2015

erudne said:
1st disassemble and dry lube your mag, check mag catch to see if the catch is screwed even with the release button, check for burrs and dents in mag. Lube your recoil spring w/lithium grease. inspect your bolt and bolt locking recesses for burrs etc. Gas key correct? Is your ammo reloaded?
If the above are to spec try to locate an adjustable gas block and install.

Will give it a try.

bakersman345 · Nov 21, 2015

File down the m4 feed ramps to make a smooth feed ramp like the ak-47 has. Buffer spring mine was too light to chamber the next round

Member 5605 · Nov 21, 2015

after fired will it lock the bolt back?

GMC Z · Nov 21, 2015

GMC Z said:
Will give it a try.

Problem solved. Fired it with a single round, the bolt did not lock back. Did a full mechanical inspection, lubed the mag and buffer. No joy. Gas port was .094 opened it up to .125. Everything's running like a well oiled machine. Thanks to all.