I took my LMT to the range Sat to zero my aimpoint with PPU 75gr loads. I loaded a 20rd Lancer and 3 20rd PMAGS. I used the Lancer first, hit the bolt release and fired away. Bolt locked back after the last round. I next loaded PMAG #1. Hit the bolt release and…nothing. It wouldn’t release the bolt. I used the charging handle and everything worked OK until the last round, the bolt didn’t lock open. Loaded up PMAG #2, same thing with the bolt release and I really smacked it this time too. Also, bolt did not lock open after the last round again. Loaded up PMAG #3. Still the bolt would not go forward using the bolt release lever. I ejected the mag with 10rds still in it and loaded them in the Lancer. The bolt release worked fine and the bolt locked back after the last round. I’m using an H buffer in the LMT and all the mags were loaded with 20rds. I’ve never had any problems like this running 30rd mags, Lancer, PMAGS and GI mags. Any ideas?
When you say that you hit the bolt catch with the PMags and nothing happened, do you mean that it would not move? Or that it would move like it was releasing the bolt but the bolt would stay in the rearward position?
My 20 rounders randomly fail to lock back. I still need to test with proper mil-spec ammo, I’ve been shooting cheap Centurion and gun show reloads to get my sights on paper.
I have the same issue with my 20 rd Pmags and my LMT rifles. It usually takes some force on the bolt catch release to make them work. You could try taking the upper off and inserting the Pmag to see if it is interfering with the release interface and then compare it to your USGI/Lancer mags.
I pressed hard on the bolt release lever and it wouldn’t move.
Give this a try. See exactly what’s preventing the bolt catch from moving.
my problem happens with my LMT rifle and my Centurion/noveske/BCM frankengun. I’m going to try some other ammo, then give Magpul a call. Make sure you give LMT and Magpul a chance to resolve the problem as per forum rules. FWIW I don’t have this issue with the 30 rd PMAGS.
LMT? That’s a feature.
Had the same issue with a couple of PMAG 20’s in my AR as well, (Denny’s Lower, BCM upper). Turns out that there is a slight hump in the PMAG that the bolt catch had to override, and it was a little pronounced on the 20rnd PMAGs.
I sent MagPul an email, and they replaced the mags. No issues with the new ones.
ETA: Before contacting Mag-Pul, I shaved the hump on one of the mags, and it also solved the issue, but Mag-Pul replaced both mags (paid shipping both ways too).
That’s exactly what the problem was (the bolt release anyway). I shaved a little bit off each one with my knife and they worked fine. I also checked an older Black PMAG I had but that worked fine as is. Before I shaved them I also checked the mags in my Bushmaster lower, same problem with the bolt release. However they worked fine in the S&W lower with my B.A.D. device attached.
Thanks for the info.
I’ve heard of this anomaly, but never experienced it myself, and I use 20 round pmags exclusively.
Flawless operation for me in both Bushie and a S&W lowers.