and shooting a guy in the leg to poison them is more effective then say...shooting them in the face?
Effectiveness is dependent on your goals. If you want'em dead "like,
right freakin' now!" then a headshot with a massive caliber might be your best option. On the other hand, if you're in the "trying to send a message to a group" sort of thing I can see where an airgun with a dart like they use to anesthetize animals (only loading the dart with something lethal
but slow acting) would be the option of choice.
As for the difficulty of making them...oh, puh-
lease...hollowpoints, poison, and a candle. Child's play, workbench not needed.