I have to agree with Bramble on rethinking his choice of weapons. If their is a problem than having a repeat while trying to shoot an Elephant would increase everyone's pucker factor.

It also sounds like his gunsmith didn't inspect the case well enough or he would have noticed the ringing. Not very professional.

I have had similar ringing problems with Norma Brass in 9.3x74R and the case heads does separate. I can't believe that is what caused the rifle to spring open though.

How many rounds has he fired? You get a feel for a familiar rifle being right. I would have thought an action that was not locked would have been noted by the shooter.

Send the rifle back and pick another for the trip. Also shit can the brass and just save the bullets.