I reload my own .44 Special and .357 Magnum shotshells with #11 shot. I'm pretty confident either is adequate for snakes at 10 feet or less. Speer says the spinning shot column spreads at a rate of about 1" per foot, so it's not a long range proposition.

CCI loads the Speer shot cups with #9 shot. I like the improved density provided by the smaller #11 shot. YMMV.

CCI cautions against using shot shells in any handgun with porting.

CCI Ammunition - Pest Control/Speciality