"Tell your friend to lookup up the London Proof House. (worshipful company of gun makers...I think that's the full name) They do post mortems on failed guns and their opinion would be irrefutable by comparison to an American metalurgy expert. "

I'm not an attorney but even I know that the litigation would be subject to the Laws of the Country in which the failure occurred and to say an opinion by the Proof House would be irrefutable is folly. If you want to even have chance you will need a failure analysis with all the bells and whistles with academic credentials to back up the analysis, and that is a Metallurgist usually connected to a University. I haven't participated in a lot of this type of litigation but have conducted a LOT of failure analysis in the Nuclear Power Industry.-Dick