Practice a lot with hexnuts on a fork you don't care about so much, then when you suffer no fork hits, practice on the fork you want to hunt with. My first boardcut died prematurely from a hexnut forkhit. Alternately, use a metal, polymer, or high tech laminate fork. They are unaffected by just about anything you can fit in a slingy pouch.
As far as hunting ammo, you want something heavy and cheap. I can't find much that costs less than a stack of 7 US pennies. Even sizeable hex nuts cost more than $.07 a piece.
ultimate: I think Xanthos is making a compound statement. First, he doesn't approve of hunting. Second, that hunting with a slingshot is illegal in Germany. Can't say from his post whether he approves of a ban on hunting, just that hunting with a slingshot is illegal in Germany. I disapprove of Kathy Najimy and Queen Latifah not finding me attractive, but I wouldn't support legislation saying they have to!
Depending on bands ofcourse (i use looped dankung 2050 on a rambone fork) but 12mm lead balls i find an amazing combination. Very accurate, fly straight and very fast. And because of the weight (around 12grams) the energy on the target makes them perfect for all small game. And you can buy a 12mm fishing mould for around £10 and cast up around 1000shots for £10 of lead scrap if you make friends with your local scrap dealer. Thats my preference anyway. Hope it helps.