you need to have a gunsmith who knows double guns examine the bores to make sure that the former owner didn't remove a lot of barrel metal from the bores in order to get the gun "ready to sell." Sometimes nice shiny bores are shiny and nice because someone has honed away a lot of rust and pitting and left the barrels too thin to handle modern ammunition (and sometimes even the original blackpowder ammo, too).
Any gunsmith with the tools to measure the ID of the bores and the reference books to show him what the minimum amount of barrel thickness is needed to be safe can let you know if you should be shooting this gun.
Welcome and I hope you are soon "cowboyin'" like crazy!
