Originally Posted by JonnyV
They also don't come out all that easily when I pull on the charging handle. Takes a few smacks on the buttstock to get them to come out.
I still think you're collapsing the shoulder and trim length doesn't have anything at all to do with this problem.
To see where the problem is take a round that had these problems and paint the whole thing with a magic marker.
Jam it in there again. (Follow all safety practices, of course, muzzle in safe direction, etc.)
Get the round out of the chamber and see where the ink has been scraped off. I'll wager it's around the bottom of the shoulder.
And no. There should be no need to use a crimp for AR rounds. If you do crimp be sure you are crimping into a cannelure on the bullet or you risk collapsing the shoulder with most crimp dies.