Do not shoot any smokeless powder out of it, they make black powder shells for the Damascus guns. Cleaning afterwards is a pain. Modern ammo will blow the gun to pieces!
This is always a good idea with any old gun. Modern powder generates much higher pressure than black powder, the old guns simply can't handle it. They can and have blown up in peoples faces. As far as slugs go, your old gun will have a choked barrel, meaning it gets narrower toward the muzzle, a slug could very easily jam in the barrel and turn it into basically a pipe bomb.
Having said all that, I've shot a lot of old guns like that and I like them a lot. I know what to look for though to make sure they are safe. Most local gunshops will look them over for you, often free of charge, but even if it costs a few bucks it's worth it to be safe.