I’m new to AR’s and just built my first through PSA with a Complete Upper and Complete Lower Build. (PSA 16" MIDLENGTH 5.56 NATO 1:7 NITRIDE 13.5" LIGHTWEIGHT M-LOK UPPER WITH BCG, CH, & MBUS SIGHT SET / PSA AR15 COMPLETE MOE EPT STEALTH LOWER, BLACK)
I just got out to the range today with a NRA instructor for a basic carbine class, and while shooting we noticed the bolt was not locking back when the magazine (30rnd MagPul Gen2 PMAG) was empty. We could lock it back manually with an empty mag in, but it would not do it automatically when last round was shot. We separated the upper and lower to investigate, but nothing seemed out of place, so we just oiled things up to see if that would help make things run smoother. It did run smoother and locked back a few times after, but it was short lived and stopped doing so as we kept shooting.
Does anyone have any insight on why this is not functioning properly?
If so, what can I do to make it function properly? (Besides keeping my gun soaked in oil.)
Or is this just something that may self-resolve as more rounds are put through it and broken in? Put 210 rounds of 5.56 through it today, using 7 different PMAGs, to see if it was a magazine issue as well. Made no difference currently.
Try a different mag, preferably a metal GI mag. Sometimes ar’s just like specific mags and not others.
You can check the contact between the bolt catch and the mag follower by inserting an empty mag with the upper off. Also, make sure the mag catch moves freely and is not binding with the roll pin in any way.
Frontier 5.56 55gr and 62 gr FMJ. I did try different mags throughout the day, some worked some didn’t but they were all MagPul Gen 2 PMAGs. I was wondering about the gas pressure. I’ll have to check into it.
when I first got my x39 AR I took it to the range and the first shot refused to extract. Took some work but I got the case out and tried another. Same thing, wouldn’t extract. I figured I would take it home and give it a once over and when I picked up the rifle the gas block slide right down to the flash suppressor. I had purchased the gun from my dealer who got the gun from an estate sale, the guy that put the upper together used flat set screws. No dimples, no cups. Check the gas block, check the bolt, check the buffer, check the buffer spring. I figure it’s either under gassed or the buffer is too heavy.
My new x39 AR was not cycling back far enough to strip the next round. I took the gas block off and noticed the port had some burs in it. I took a same size drill and cleaned it up. That got it to about 50/50 I took the next size bit and very carefully opened it up with that. It all of a sudden was 100% for 100 rounds.