I've done it. I have a short barreled P22, the long barrel's performance should be similar.
The CCI shotshells won't cycle the slide, but they chamber nicely from the magazine. It goes ka-POP and sort of halfway moves the slide, but not enough to eject and rechamber (but it also doesn't jam mine, oddly enough).
Mine threw about a 2 foot pattern from the muzzle to the ground, a total distance of about 5 feet the way I was aiming it. I took a shot at an empty gatorade bottle just to see what the stuff would do. The pellets went through one side of the bottle and left little dents in the other, but a handfull (maybe 15) got stuck inside the bottle. The rest went everywhere.
I imagine it would cause a snake to back off long enough for you to leg it but it probably wouldn't kill it first shot (or maybe even subsequent ones). Keep one snakeshot load in your chamber and the rest regular ammo - that way, when you sting up the snake with the shot (head shots are most effective) and it turns into what was accurately described as a "writhing ball of snake, not interested much in striking" elsewhere on this very forum, put a regular slug through its head if you're the humane sort, and beat feet if you're not.
