When i was in Africa i had a run-in with two black cobras, very very large snakes. Their bite can essentially kill you in a matter of hours, if they release the venom. My driver was going up a mountain at night and the giant snake was crossing the road. Well, I would dare not shoot this thing with anything that would not bring instant death and guaranteed to hit, since they are extermely fast and stealthy. Well, my driver was daring and he went full speed and smashed the snake with the car. Problem solved. However, I heard later this was dumb, since they can jump into the under carriage of the car and find a way into the vehicle. It has been known to happen. In Africa, they have a major problem with pythons, as well as the cobras, vipers and puff adders, and the cattle nomads where I lived would kill them using their shotguns, I suppose with a buckshot round. Pythons are real huge though, not as hard to hit.
Anyhow, rattle snakes, especially the eastern diamondbacks canbe very dangerous. If you get a bite to the head, you can be as good as dead. I would certainly make it my business to kill the damn thing if it was in my yard. If you have enough distance, wouldn't a .44 with a scope be quite efficient? If you are in town, I guess you cannot go that route. How about a 9mm with a silencer?
I jump back up and realize when I get to my feet that my left knee was not working. By then the snake had turned and took off into the woods, but I managed to keep the flashlight on it until my son got back with the shovel. Limping on one leg and hanging on to the trees for balance I managed to kill the snake.