Weird problem with bolt not locking back

[bimmer]

Took the Daniel defense out today, and with the supressor on, the bolt wouldn't lock back after the last round. I knew that it was probably just over gassed, so I figured I'd just put an H3 buffer in until I get an adjustable gas block. I took the supressor off, to let it cool down a little bit, and shot a mag through it without the can, and the bolt still didnt lock back. I was using a 20 round pmag both times. I then tried two 30 round mags without the can and it worked fine and locked back. I put the can back on and shot 3 rounds out of each 30 pmag and it locked back with both. Then I put the 20 in with 3 rnds, and It didn't lock back. I tried all three of them about 3 more times and had the same outcome every time, with and without the can. Then I tried a 30 rounder with a ranger plate on it, and it would not lock back. Tried I different 20 rounder and it would not lock back. I only brought the 5 mags, so I didn't have a chance to try any GI mags, or other Pmags. The 20 rounders were brand new, and purchased in December. They came with dust covers, and in the clear ziplock like bags, so not sure what gen they were. The 30s were all gen 2 I believe (idk if it matters).
any idea what the problem might be?

[Great-Kazoo]

Took the Daniel defense out today, and with the supressor on, the bolt wouldn't lock back after the last round. I knew that it was probably just over gassed, so I figured I'd just put an H3 buffer in until I get an adjustable gas block. I took the supressor off, to let it cool down a little bit, and shot a mag through it without the can, and the bolt still didnt lock back. I was using a 20 round pmag both times. I then tried two 30 round mags without the can and it worked fine and locked back. I put the can back on and shot 3 rounds out of each 30 pmag and it locked back with both. Then I put the 20 in with 3 rnds, and It didn't lock back. I tried all three of them about 3 more times and had the same outcome every time, with and without the can. Then I tried a 30 rounder with a ranger plate on it, and it would not lock back. Tried I different 20 rounder and it would not lock back. I only brought the 5 mags, so I didn't have a chance to try any GI mags, or other Pmags. The 20 rounders were brand new, and purchased in December. They came with dust covers, and in the clear ziplock like bags, so not sure what gen they were. The 30s were all gen 2 I believe (idk if it matters).
any idea what the problem might be?

You answered your own question.
Usually bolt doesn't lock back from being under gassed, or too heavy a buffer, OR incorrect recoil spring. You're messing with too many things. I'd be doing mags before any changes to gas block, or other internals.

Try GI mags. While a nice product, PMags are far from perfect, in my case to the tune of 1/2 dozen. That number reflects the one's i have used.

[colorider]

I have 3 20 rd pmags that cause the same problem you are having.

[bimmer]

The thing is the mags worked fine in my BCM. Forgot to mention that.

[Fentonite]

Had a similar problem. I put in an H3 buffer, and it has been flawless since. YMMV.

[Great-Kazoo]

The thing is the mags worked fine in my BCM. Forgot to mention that.

Suppress your BCM. All that takes is swapping flash hiders / suppressor mounts

[Sharpienads]

I'll bet it's the mags. A lot of people have had issues with 20 rounders not holding the bolt back on the last round, including somebody on this forum. Your BCM and DD bolt catches might be different sizes, too which would explain why the follower pushes one and not the other.

[Sharpienads]

Here's the other thread, with a link to a different site that has a good explanation of the problem.

https://www.ar-15.co/threads/90119-B...hlight=pmag+20

[Great-Kazoo]

I'll bet it's the mags. A lot of people have had issues with 20 rounders not holding the bolt back on the last round, including somebody on this forum. Your BCM and DD bolt catches might be different sizes, too which would explain why the follower pushes one and not the other.

IMPOSSIBLE Magpul, like CLAPTON, IS GOD

[Sharpienads]

IMPOSSIBLE Magpul, like CLAPTON, IS GOD

You are correct.