I took a lot of bunnies with a slingshot and they were clean kills (and good eating). First good one was a wooden one my Dad made me from 1" plywood, surgical tubing, and a pouch from a leather shoe tongue. Had to know how to repair the elastics on that one. Much later, a wrist rocket and frankly, that style (braced) is a lot easier to be accurate with.

I used industrial marbles for serious ammo - they were really cheap and there was a local source for bulk purchases (minimum 1000). Acorns were great for messing around with. River pebbles are a closer range proposition - too inaccurate compared to marbles. I used some 36 cal lead balls from time to time but really, the marbles were the best thing for hunting IMHO.

Long time ago... they have better commercial slingshots now. Carry a spare set of elastics, though.