Just some general observations. Spelled out in Louisiana hunting regs. is that during BP or archery season, the only cartridge gun allowed is a .22 loaded with rat shot. We have a lot of snakes., and not being allowed a centerfire, .22 rat shot is "it".
It works better from a pistol than a rifle (but best from a smoothbore rifle...that's just not allowed during those seasons).
Pattern runs out of snake killing at about 10 feet. More power wouldn't help, it's the pattern that suxs from a rifled barrel. this works out OK, as if the snake isn't closer than 10 feet, i'm not going to shoot it anyway. If it's slithering over my boot, will wait for it to get 5-10 feet away before shooting it (becasue i don't like to limp).
A really big snake is going to be PO'ed, but generally balls up and forgets about you. Plan of a revolver and shooting 3 or 4 times.
The old crimped brass loads work better in a revolver for me than the CCI plastic capsule type. CCi's uses larger shot, but power isn't the issue, pattern is. BUT the crimped brass cases tend to stick in some rifle's chambers (the unfolded brass case is long enough to have it's end be ahead of a typical chamber).