On Kentucky Educational TV, there is a fellow (Last name is Farmer) who hosts a hunting/fishing show called Kentucky Afield. He apparently has only one arm but shoots a bow using a tab of some sort which is attached to the string and he pulls it with his teeth---he is pretty darned good with that thing too.
It looks to me like a piece of lether which is doubled around the string and perhaps sewn there. He bites down on the tab, then pushes the bow away from himself out to full draw, and when he is on target, he simply releases. I don't remember if he uses asight or not.
He shoots a shotgun with his left arm only----but he actually mounts it to his right shoulder and his left arm is across his body. Looks awkward as heck to me, but again, he is a darned good shot. He doesn't let his handicap hold him back at all.
Joe