As a person that has a few snakes as pets (yes, I really do), if you have time to draw your weapon and blast away at a snake, you have plenty of time to walk away from the "threat". Rattlesnakes across the country are becoming more rare becsause of "the only good snake is a dead snake" philosophy. Rattlesnakes do more good than harm to the enviorment. They eat rodents....lots and lots of rodents. They also wish you no harm. The people that have been biten by rattlesnakes were bitten either because they messed around with the animal, stepped on it, or stepped very, very close to it. Leave them alone and they will leave you alone.
BTW, unless you get a clean headshot with several pellets entering the brain, you will just piss off the snake making it much more dangerous, and if it crawls away, you will have resigned it to a slow, painful death. Deer hunters have a code of ethics about clean kills and no wanton waste....shouldn't this apply to other animals as well? Sorry for my "rant" but snakes aren't "evil".