Quote
chambered in 300 win mag
You gotta use enough gun to do the job, man. You risk a pea shooter like that on dangerous game? grin

I would play around with some empty cases to see what circumstances will cause it to jamb like that. My 1st thought is what you thought - some crud had got in the action.

“In a time of deceit telling the truth is a revolutionary act.”
― George Orwell

It's not over when you lose. It's over when you quit.