For snakes, would go with a .357 revolver w/ shot loads- I do my own with #4 shot, and the Speer shot capsules.
MOST autos will not cycle semi with shot- the projectile does not weigh enough to give an action/reaction adequate to overcome the spring tension. Long, long ago, in a galaxy far, far away, I used to make my own 45 ACP shot loads that WOULD cycle- but they started life as a 30-06 cartridge case- cut, sized, and using a gas check as an overpowder wad. Painstaking to load, but could impress the daylights out of fellow hunters on quail!
IMHO, just about ANY rifled firearm will have limited range with shot loads, since spin imparted by rifling gives a "doughnut" effect to patterns beyond a few feet. If lead shot "hurts" your barrel, one cannot but wonder what the heck the barrel was made from- cookie dough? Loads in a plastic shot capsule may leave some plastic fouling- but 2 minutes with a bore brush fixes that.