Well, if it's a .45, the "correct round" should be .45 Colt, also known as .45 Long Colt; however, you might get slightly frustrated by the Wal-Mart clerk when he can't seem to find where they store their black powder .45 Colt rounds.
Yes, if you're going to fire it, it's really playing with fire to shoot anything other than black powder rounds. I have .45 Colt SAA's (Peacemakers) from all three generations, and I shoot virtually nothing but black powder rounds in all of them. I stuff 'em myself, though, by the thousands.
I shoot everything under the sun, but these are my favorites.