In my experience when a snake is shot with a shot shell from a handgun it usually doesn't kill them. However, they coil themselves into a ball or big cluster allowing for a 2nd shot with a regular round to finish them.

One other note on shot shells. Don't make the mistake I did. I usually take my home made target stand with cardboard backer for short range testing. One day at the range I didn't have it so I stapled my shot testing target to the particle board at the range. I took a shot from 5 steps away and most of the load ricocheted back in my face. Thank God I had glasses on.