Not an expert, but kind of looks like a Colt M1877. Made from 1877 to the early 1900's. Made in several calibers and barrel lengths. Pretty rusty, but you might check out some pictures on the net and see if it matches. I think Billy the kid used one. good luck with it. Good find!
Does look like one except for the trigger bow and depth of the frame. And the spur at the top of the handle. And the wood grips of the 1877. Though the 7-1/2" barrel of the M1877 was 2" longer than his whole find. Shortest I could find was a 2-1/2" barrel "snub nosed" version.