The .45 Colt is a popular choice for the SA revolver, but whether or not it'd be the caliber for you depends on whether or not you plan to handload. The .45 Colt, even at standard SAAMI-spec pressures, is a extremely versatile round, capable of pushing 165 to 300 grain bullets, with the perennial favorite being a 250 to 260 grain bullet humming along at 900 to 950 ft/sec. Most commercial-manufacture ammo for the cartridge is aimed squarely at the "Cowboy Action" market and features a 250 grain bullet at 750 ft/sec. SD loads are spread out between 200 grain bullets at 1000 ft/sec to 250 grain bullets at 800 ft/sec. Even then, recoil is noticeably heavier than what you'd find out of some .357 Magnum loads (more of a shove, without the bark and blast of a .357 Magnum.)
Guns range from inexpensive Italian clones of the old Colt SAA, to American-assembled guns made from Italian clone parts, to Ruger Blackhawks (which, while having very little to do with the Colt SAA, are tough guns which will handle loads that would scatter any Colt SAA or clone) to American-manufactured clones of the Colt, to actual Colt-manufactured SAA guns, which are rather . . . pricey.
If you don't plan on handloading, single-actions are also made in .22 LR if all you want to do is punch paper and shoot the odd rabbit or squirrel, and .357 Magnum if you prefer centerfire with some versatility, without the acute financial pain of buying commercial-manufacture .45 Colt or other "big-bore" ammunition.
