I gave up on shooting at snakes many years ago, if they actually need killing there are far more effective tools.
Good for you, the key words are "if they actually need killing". I haven't killed one in over fifty years, despite having spent huge amounts of time in the outdoors. I won't kill a snake unless it's him or me. It hasn't been him or me since that time decades ago, if in fact it was then. They're part of the Big Picture, with their own jobs to do--like keeping down the rat and mouse populations, for example.
I have some .38 Special shot shells I bought years ago, but only because an LGS owner tried to convince me they're devastating up-close SD rounds. I wanted to test them because I thought he was only trying to sell shot shells (still think so). I've never carried them, and won't unless we have an invasion of rats in my neighborhood.