Let us face fact, someone out there has already made a modification that would be heavily frowned upon by most on this board.
I'd simply extend the chambers to 2 3/4" if the wall thickness is robust (never seen a French gun that wasn't) and call it good. Mike Orlen could sneak a choke tube in one or both barrels as well, should you want a bit of choke.
An occasional promo load wouldn't likely hurt a thing, except, perhaps, your shoulder.
Most of the conscious bet wetting and hand wringing that goes on here, in regards to short chamber guns, 2 3/4" loads in 2 1/2" chambers, high versus low pressure, whatever, is a moot point with French guns.
Have the WT measured. Lengthen to 2 3/4, assuming it has not been modified or honed, and keep on keeping on.
Best,
Ted
