The rounds not going all the way into the chamber was the give away. Classic no powder charge. The primer had enough power to push the bullet out and all the next rounds hit the bullet in the barrel until it was pushed fare enough forward to allow a round to chamber.
A good lesson to never assume something and to stop and investigate before things go bad. I witnessed this same thing except it was a hand gun. I suggested to the shooter to stop and check his weapon, but the dirty harry told me to buzz off. Well I rapped harry's hand in a rag from my range bag as I walked him out of the range and to the ER to get custom 1911 wood splinters removed from his hand.