Some are known and obvious:
[ol]
[li]Bad ammo
[/li][li]worn extractor
[/li][li]tight/wrong chamber
[/li][/ol]
What else? Let’s say you’re shooting known good ammo that works in other similar guns, you’ve reamed/checked the chamber, and the BCG is brand new BCM FA group and passes all visual inspection. What else?
Even if the chamber, ammo and extractor are in good repair, I wonder if hot ammo could case extractor jump? It’s a rare problem in pistols with +p+ ammo. So, I guess a over gassed gun maybe a cause and contribute.
When we had the 3rd gen SW’s, we would experience it once in a while.
Is the fired cartridge left in the chamber and a new round loads into the base?
Correct buffer for the configuration.
Action spring in spec.
Try a known good BCG in there to rule out a problem with the new bolt/extractor.
Check the fired brass for signs of a rough chamber.
Check the gas port, it could be the wrong size.
Correct. And once the loaded round is cleared and magazine ejected, if the bolt is dropped it resists mortaring and has to be cleared by bashing charging handle on the bench/table.
Interestingly this issue presented itself after changing to a buffer of identical weight but different internal makeup. BCG has been replace with known good example, but good call on the spring. Will check and report back.
Carbine/ammo combination known good prior to issue surfacing.
Make sure the chamber is clean.
Steel cased ammo and or lots of suppressed shooting can build up a very hard layer of carbon in the chamber. Sometimes I can still find some in the chamber with a borescope after what I consider a normal amount of chamber cleaning.