[Cloud William]

It sounds more like they've bored a small hole through the chamber wall and then inserted a plug which has the "die" on the end. The brass case expands against the chamber wall, engraving the mark before the pressure drops and the extraction cycle commences.

IF that is what they did, they are going to end up sued into oblivion when their invention causes a catastrophic failure (KaBoom).

I don't care where they hide the thing... I can find it and obliterate the stamp. It's a foolish idea, akin to the "Safety Bullet" that was the topic of heated discussion here a month or two ago.

[RightWhale]

They might be doing some high tech stuff. Might be interesting.