It was a cheap generic bolt release.
Pmags and GI mags interface with the bolt catch differently. When the catch is damaged or becomes misaligned, often one type of mag will work while another will be problematic.
Printable View
I never knew this, thanks so much for sharing.
Because everyone was on pins and needles about this, here’s an update.
Popped out the bolt catch for inspection and cleaning. Cleaned, changed the spring, and reinstalled. Nothing seemed whacky but...
Also noted the bolt failed the gas ring test. A little surprised because this bolt/BCG only has about 1000 rounds through it. Replaced the rings.
Shot several rounds today and had zero issues. Good lock back on all mags. Issue resolved.
Sent from my iPad using Tapatalk
Good to hear, thanks for the update.
Maybe I read it wrong. Weren't there two complete uppers that were having the same issues? Both bolts had ring issues? This whole thread I have been wondering about the mag catch, somethings allowing G.I. mags to work but not Pmags. Wouldn't worn rings fail on both mag types?
No. Only one upper with the issue - wouldn’t lock back on PMags, would lock back on USGI.
Not sure if the worn rings had anything to do with. I hadn’t even thought to check the rings because of the low round count and lack of any symptoms of worn rings. Caught it during a more thorough inspection before shooting yesterday.
Worn rings and a minor issue with the catch probably combined to cause the issue. As was said earlier, PMags have a little different geometry. Probably just one of those strange combinations of a few small things. Sometimes it happens.
Sent from my iPhone using Tapatalk