The problem with it is that your pistol, and most pistols for that matter have rifled barrels which impart spin to whatever is pushed through it by the expanding gasses of the powder charge.
The effect that this has on shotshells is that the shot expands in all directions as it leaves the barrel, due to the size of this shot, the one or two pieces that hit the target may have little or no effect.
I experimented with .38 shotshells a couple years ago and fired them through a "tunnel" I made by joining two plastic 5 gallon buckets together and cutting out one of the bottoms (essentially making one 10 gallon bucket). The handgun I was using was my 4" S&W 686.
I fired one shotshell toward the center of the bucket. 80 to 85% of the shot impacted on the sides of the tunnel while the shot that hit the intact end of the bucket was mostly spread toward the outer edges, the plastic cup that holds the shot exploded as soon as it left the barrel as evidenced by pieces of it embedded in the sides of the tunnel. only three pieces of shot hit near the point of aim (actually within a 3 inch circle).
For snakes you would be best to use a smoothbore like a real shotgun, or you could buy a cheap 38 with a shotout barrel or have someone bore out the rifling and use that just for snakes (there may be some legal problems with the last option).
After I finished shooting the whole package I never bought any more. I carry a .410 shotgun and a .45Colt when I think I will encounter snakes.
