Just a thought Drew. I wonder if it worth sending the picture by e-mail, together with all the known facts, to one of either of the British Proof Houses. I've always found the one in Birmingham most helpful and they have been involved in this sort of stuff for over 200 years. I would be certain that they will have experience of exactly the same sort of failure. Ideally they would want the gun and remaining cartridges but I should think that they could offer an educated opinion at least from the picture. They are probably the greatest experts in cases like this and do undertake investigations and provide detailed reports as part of their service to we shooters here. Lagopus.....