My stepson had a surgical tubing slingshot...I gave him some wheel bearings which were almost .50 caliber mini balls. The way they wripped through the woods...I have no doubt it was lethal.
Another one that will surprise you is the blowguns with spring wire tips. Wicked on rats.
And never underestimate the power of a 177 cal. pump up pellet/BB gun. Year before last I killed 4 snakes in our implement shed with one. 3 of the 4 were rattlers. Got 3 the first day and the straggler the following day.
The day before I found the snakes in the barn, I was using a hand truck and railroad pry bar to move a 500 lb. barn door that was blown off the trolleys. I was using the hand truck to raise and slide the door as my helper walked the other side with the pry bar. I almost pushed the door to point of exposing the rattler. I removed the hand truck and turned it over and used the lip of it like a hoe. Smacked the crap out of him and penned him down calling for my helper to come kill him. We got it done.