I remember Venturino writing an article that stated #12 is the bomb-diggity for snakes.
Travis
Because 12 is so hard to find, I bought a couple of boxes of cheap Rio 12 gauge loads to cut open for the shot. I think I paid about $2.50 a box. I'm about half way there, with the capsules loaded, but not the cartridges yet.
The shot varies in size a lot, but there sure are a lot of them in one shell.