Most French guns have stout chambers and muzzle wall thickness. While you should always measure (Gene’s anecdote about a guy who KNEW the chambers were thin, and lengthened them anyway, demonstrates that not everyone who has gun smith tools should be allowed to use them) it has been a long time since I measured a French gun with less than .050 wall thickness, and a bunch of metal in the chamber/forcing cone area.
If you find that, you could certainly consider lengthening the cones, or, the chambers, or both. I’ve done it, told people to do it, and, sometimes just not done it, even though I think I could. Depends on the gun and the use it is going to get. I have a single, French, 2 1/2” 12 that I am using as is, mostly because there is a flat or so of 2 1/2” stuff on the shelf, and I intend to chase pheasants in the cold with it. That, and I’m cheap, and hope that 2 1/2” ammunition returns before I’m dead.
Might not, though. We will see.
Best,
Ted
