I have a BCM upper and I’ve had problems with my bolt locking open after firing my last round. I think it has something to do with the pmag followers getting nicked somehow. 
This is how several of my followers have become recently. Anyone know what could be causing this?
That nick shouldn’t be causing issues with the mags failing to lock the bolt back.
Have you tried other mags in the rifle to see if they hold the rifle open? Also, what ammo are you running? Lower? Buffer? More information could be helpful.
ON a related note, I have had Tula fail to lock the bolt back on several of my rifles, BCMs and even an over gassed Bushy because it wasn’t cycling hard enough. Could be the ammo. Could be that the rifle is over sprung, could be several other things as well.
Well it locks back with other mags, I cannot remember what ammo it was. Department issued, it’s a spikes tactical lower, and a standard weight buffer
A little more info. Upper type, buffer and spring, etc… would all be good.
I have run into a few Pmags that would not hold open after the last round was fired.
What I found was the top of the rear spine just below the “U” or “V” channel had some plastic flashing that when the magazine was in place would make contact with the bolt hold open and not allow the spring pressure to push up and lock back.
Took a razor knife and trimmed the flashing so it did not make contact with the bolt hold open and all is well.
Worth a look, just separate your halves and put a magazine in and toggle the hold open and see if there is contact.
Clarence
I’ve had this happen with a few Pmags as well. I took the mag apart and used a small square file and reshaped the opening from a rounded off “U” shape to a defined square shape and the problem was solved every time.
Can you explain in a little more detail pls? Or even just a picture
On gen 1 and 2 pmags the U shape on the top rear of the magazine body has a little flashing that can rub against the bolt catch. It will contact the wider portion, not the little tip that rests on the follower. This prevents the follower from reliably pressing the bolt catch upward after the last shot.
Refer to the first picture in this post by Pandamonium: https://www.m4carbine.net/showthread.php?88910-PMAGs-not-locking-bolt-open-figured-out-why&p=1120823#post1120823
Original on the left, modified on the right.
Never had that happen. Is it a definite mag issue, or is it something more?
Well it was only happening with these mags
Tagged, for info. Thanks.
Well I have done this little trick to all my mags and am still occasionally getting the fail to lock open after last round. Anyone else have any ideas?
I’ve had the occasional bolt catch that was too fat for the slot in the receiver but I highly doubt that’s the problem. It look’s like a mag issue with what you’ve described. Take another look at them.
Which bolt catch did you put in?
I do not know how far you have gone in resolving this issue. However, in addition to filing the U shape into more of a square have you tried to file the side angle profile? I usually file the side profile also, and use the Gen 3 impact/dust cover as a template. Once the Gen 3 side cover snaps into place on the Gen 2 Pmag I have altered the magazine far enough.
