The way I see it, it doesn't matter what size the snake is as long as the 12 gauge shell will fit in the chamber. Once that happens, it's generally just a matter of time.
I'll say this much though, if I ever lay eyes on a snake the size of that thing, you-all south of the border will see the results on the evening news, and some might even hear the gunfire if it's a quiet kinda day. Might call for some 3-inch medicine and some #2 shot. He**, if I have buckshot lying around, that critter is a good candidate !
Sean