Plus one for Mike - price is far too high (although I am in the UK~)

Not to say a .577 2 3/4" is not viable in a Martini but I would be very careful about this one

I have a double .577 3" (posted here somewhere), a good cartridge but at that early time not quite up to the bore rifles for dangerous game in cover

Good luck whichever way you go

TH44