Ist gen Hammers had a conical rigid firing pin. 2nd and 3rd gen hammers vary in height and shape, some have floating firing pins with a concave profile. The 1st gen hammer and trigger/bolt screws have a different thread than the 2nd or 3rd, and are domed more on the head surface with a wider slot.
The 1st gen barrel has a .695-20 tapered thread, similar to a pipe thread, designed, probably to self center in the frame. ist gen ejector housings were different, and early rifling was deeper for black powder, and some had no stud for the ejector housing. bore diameter was .454.
Postwar bores were .451-.452 diameter, like the M1911.
2nd gen barrels also had the tapered .695-20 thread, but different markings.
3rd gen barrels have a .695-24 thread, straight (untapered).
The cylinder rachet on the 1st gen is machined differently (curved surface) than the 2nd gen, and the hand is slightly different to match.
3rd gen cylinder rachet is even more simplified in machining and the hand is quite different, and not interchangable with the 1st or 2nd gen hand, if the cylinder is changed from a 1st or 2nd to a 3rd gen cylinder or vice-versa, the hand must be changed as well.
3rd gen cylinders, until very recently, do not have the removable cylinder bushing as do the 1st and 2nd gen guns, but recent production as revived the design. 3rd gen gas ring (bushings) were pressed in place.
Early 1st gen revolvers had the "black powder" frame, the pinched frame, "V" notch rear sight and thinner front sight. The cylinder pin was retained by a screw in the front of the frame.
Later 1st gen guns adopted the tranverse cylinder pin release, used on all subsequent guns. 2nd and 3rd gen guns all have a square noitch rear sight and wider front sight.
That's a start, anyway, of the differences.
