Sarg -- graphic picture of a great point!

Sounds like (possible) crimp failure on the last round.

One of the things to push into one's training is to load from the ready supply *and* to rotate the ammunition.

I've seen discussions in a few 19th century texts the issue of pulling bullets (in the magazine or the second/other barrel) by way of recoil -- and the reminder to (when the first shot was enough) get that round into the 'first position' so that it's not repeatedly subjected to the bullet-pulling action of recoil.

Training, training, training...

Cheers
Tinker