My typical encounters with snakes usually involve cottonmouths while fishing. And if your running trot lines with my brother or uncle running the boat it's not unheard of for them to end up in the boat with you.
I always carry my S&W M18 and it's loaded with Win. Rat Shot. I keep a half dozen boxes on hand. This revolver throws a good pattern out to about 8 feet. Inside that distance I've had no problem killing any snake shot at.
The most snakes I've killed in one day was 17. I was pretty much happy to go to the house by that point.
