Luckily, he extracts his shells rather than ejects them & on this one only got the brass with about a 1/4" of the plastic case back when he extracted the spent round.!
Having ejectors does not necessarily mean that the separation wouldn't have been noticed. I trap the ejected hulls in my had as they clear the chambers. I would have noticed immediately that one of them was separated.
I do this in order to either pocket the empties on a hunt, or throw them in the trash can on a course. I'm always surprised that more people don't do this. It's so easy to learn.
