Back up a bit further...
Does it have 2-3/4" chambers or does it have 2-1/2" chambers?
Quite likely it is 2-1/2" chambers.
If you put a 2-3/4" shell into it, it will fit, but there is no room for the crimp to open and the pressures will be thru the roof.
So, if it is 2-1/2" chamber, you are talking a handload only gun.
You can use brass hulls, or you can cut the crimp off a star crimped hull to shorten the hull to 2-1/2", load it (possibly with light BP charges), and roll crimp it.
The barrels may not be Damascus, but instead be twisted steel that was hammer welded around a mandrel. I don't know how safe one of those is... no idea at all. I don't know if it was safe when it is made, nor would I have any idea how much it had deteriorated since it was made. I definitely would not go sticking a modern round into it though.
I would think that with some reducers and mounted action loads (which I believe are really just blanks), you would be in fairly safe territory.
Rick