20RD PMAG: Bolt Won't Lock Back After Last Round

[DontCome2MyHouse]

I've been having an issue where ONLY on a 20RD PMAG the bolt on my AR will not lock back after firing the last round. 30RD PMAGs work completely fine. I'm stumped. I do know the follower design b/t the 20RD and 30RD are different. I shot using an older 20RD mag and a brand-new out-of-the-box mag with the same results.

I did an experiment today. I took the follower out of a 30RD PMAG and put it into the 20RD body and it worked flawlessly. I did another test where I used a 30RD mag spring in conjunction with a 20RD follower and body...worked perfectly as well. I also test a 10RD USGI mag w/ Magpul follower and a Troy Battlemag (non-Magpul follower) and they worked fine as well.

In conclusion, the only way I can get the bolt to lock back after the last round while using a 20RD PMAG is to:

A) use a 30RD PMAG follower
B) use a 30RD mag spring w/ 20RD follower (can only load it to 19 rounds due to the longer spring, but no big deal).

Can anyone tell me what the hell is going on here? I like to use the 20 rounders for range work shooting off a bag. Through some research I have found you can NOT purchase PMAG followers, only Magpul USGI followers.

Also, is there anything wrong with using a 30RD follower inside a 20RD mag body? Seems to fit fine. I do know a 20RD follower will NOT work inside a 30RD mag body b/c the follower will not travel all the way up the mag.

[Bill.D]

Interesting, I had this exact problem with a 20rd Gen 2 half a year ago. It would refuse to lock back while hand cycling and live firing. Then a few days later, when I was about to send it back to BCM, the bolt started locking back! I have no idea what was going on and it ended up resolving itself.

My only hypothesis is that perhaps there was excess material on the follower which prevented it from rising up enough to completely engage the bolt release. My lower is a LMT and I'm pretty sure it is in spec.

[rushca01]

Known problem with the 20 rounders.

[Vec]

is this still an issue with the 20 round mags?

[Bill.D]

is this still an issue with the 20 round mags?

Mine was purchased in late November so it would seem so, but keep in mind that it is a single point of data.

[Brahmzy]

This is why there are M3 20s now. 'Mon folks! Get with the times!

[DontCome2MyHouse]

This is why there are M3 20s now. 'Mon folks! Get with the times!

Is the follower different in the M3 20rd?

[Brahmzy]

Is the follower different in the M3 20rd?

Completely different mag. It's the exact same as the M3 30, except a shorter body. Same spring, follower, baseplate... everything.

[DontCome2MyHouse]

Completely different mag. It's the exact same as the M3 30, except a shorter body. Same spring, follower, baseplate... everything.

Great! If it's just a shorter version of the 30rd it should be the fix I'm looking for. Now, if I can just find one...

[Waylander]

I have one of these from mid to late 2012. Have any of you not sent the mags back to Magpul and asked them to make it right? Maybe you don't think it's worth the money or trouble?

Have they admitted the issue?