Not a snake story, but I like to tell it.
Years ago, and it had to be between 1991 and 1995, I came home from a club meeting (it even had to be a Tuesday!) I pulled up on my hill and up to the driveway. As I parked my Jeep, the light went on in my wife's car and she was getting out. Along with our dog (he normally stayed at home.) Somethin' not right. But my fear was I would soon hear about it.
Shore'nuff. So she explained the problem. She'd moved her sewing machine up to the dining room table to work on one of her projects. Ole Spot was a dalmatian, and a live wire. He'd been riled up more than usual for a few days, but how much was just a matter of degree. After having him run between the kitchen and the living room at full speed, maybe a dozen times, she looked up. And happened to see him chasing something. It was small and furry (not a snake, a tree-rat.) So in a panic over the known deadly squirrel, she got the dog and went outside to the car to await my return.
I appreciated the confidence in my ability as a great white hunter, but of course thought it was stupid. So inside I went, and down to the basement to select a suitable weapon. As chance had it, the first 22 to fall into my vision was a M63, more than enough. Then to the ammo locker (far less well stocked than today.) I picked out some 22 birdshot, and I have no clue as to the brand. I've never seen Federals, so it probably was Winchester long brass.
I had no idea it it would kill him, or just make him mean and deadly. So Upstairs I went, with Momma and Spot waiting outside. I had no clue where the varmint was hiding, so I enlisted my trusty sidekick. Spot was more than willing and eager to help me hunt it down. He was shaking with eagerness. He didn't make it far, he stopped at the clothes closet right inside the back door. He pointed as well as a wiggling happy dog can point. So I shook the nearest coat and the coats on the far end shook. It was an open front closet maybe 6' long. So with one hand, I took the nearest handful of hangers and put them on the kitchen floor a few fee away.
Spot was still on point, so I repeated the exercise. Then I spread the coats out, but the far end was still shaking on its own, so I again tossed a few handfuls of coats and jackets on the pile in the kitchen. In maybe 45 seconds total, I had the critter cornered with very few coats left. Then with one swipe, I spread out the remaining ones. And doing that caused the little devil to show himself. But I was aiming low, between the rod and the tops of the coats, and he popped up high, over the rod. We repeated the song and dance a few times, each one my guessing wrong. Then we both went high and I had a shot. So the little kit gun went bang.
At first I thought I'd missed him. But then Spot made a lunge and had him. Something Dalmatian owners know from experience - they have a strong bite. Try to play tug of war with one sometime. You lose. I even read once where they compared bite strength, and GSDs and Pits come out decidedly 2nd best. But old spot really needed one good crunch. The critter was very dead. I think it was my superior hunting methods and shooting skills. Maybe a more reasoned guess was I was overgunned even with the 22, and I was at reasonable range, maybe 2-3' from the muzzle. Probably closer to the 2' mark.
And there was no damage we could find to the coats or Ole Spot. He was a happy doggie. He finally got to taste the critter he'd been chasing for a few days.
The only damage was to the back wall of the closet. The house on the hill was older. There was plaster with lath, no drywall. The individual pellets buried themselves into the plaster, clearly visible holes, but no flaking plaster. I didn't investigate how far they penetrated, I just filled them with a little spackling.
What I think is distance becomes the problem, and I wouldn't want to shoot a snake at 2'. I have no idea how deadly they are at longer ranges.
I do know 9mm shot shells by CCI are strong. Lots of recoil, enough to cycle an action. And at 10 or so feet they easily penetrate into pressure treated 4x4s, and 1" decking at 20 feet. I think the longer range is too far to depend on them, but I have no doubt the 9mm will disassemble a snake at 10'
If I were dealing with multiple copperheads (nasty disposition), I'd consider one of the new Govenors, or a Judge, or best of all, one of the double barrel derringers that use .410s. Those give you excess power and even a 2nd shot.