My snake gun of choice is a 480 Ruger Alaskan.
I use a 50 cal muzzleloader over powder felt wad over the powder then add approximately 150 grains of #9, and a gas check seated backwards over the shot and crimp.
A couple weeks ago bush hogging I got 2 copperheads on 2 consecutive days from the tractor seat. Four in 2 days is not a bad haul. A couple days later I got a cottonmouth about 30 inches long at the creek. Believe it or not, this is a very light snake year.

Bob