And since my wife nailed it (we have 2 small dogs), here's the recipe and the gun. I loaded .32-20 brass with 3.5 grains of unique, a .31 cal (I think it was) Ox-Yoke lubed felt Wonder Wad, almost filled the case with #9 shot, capped with an inverted gas check (.32 cal, if memory serves), lightly crimped.
I have this Colt Police Positive that came to me from my grandfather. It's a bastard stepchild of a revolver. It locks up tight, but the bore is on the rough side. The story is that Grandpa bulged the barrel somehow, so he shortened it to 3". Therefore, no front sight. It seemed a good candidate for a backyard snake pistol.
I loaded up 20, gave them a test, had my wife fire it a bit. She's a better pistol shot than I am. Beware. It's been in a kitchen drawer for several months until one of the wee mutts sounded an alarm yesterday. We don't go out of our way to kill snakes, but once in the neighborhood... Arizona is one snake shorter.