Welcome to the forum!
H&R revolvers made prior to 1904 are designed for black-powder cartridges. I dont know how to distinguish the early model American from the later, smokeless powder version, though other members here might.
What I do know from handling many, many of these over the years is that they were inexpensive guns made from rather soft metal and not designed to last thousands of rounds, sorta like the Hi-Point of their day. Indeed, they were used hard and rarely cared for. The timing, lockup, and endshake on virtually every example Ive seen is dangerously loose, and I wouldnt advise shooting one unless it were in excellent mechanical condition, using the proper ammunition ( which is rare and expensive), AND it has been checked out by a qualified gunsmith.
These are best regulated to family heirloom or wall hanger status at this point. There are many, many inexpensive and safer guns out there for any sort of actual shooting.