There is a hole in the nipple above the serial # for the primer. WHen you release the lever it flips over and fires the primer. You can't see it but there is a firing pin on the lever.
Our club has hadone like this on a box launcher for years and it works good.
Rich says do not put the bird all the way in the bottom of the pouch and it will fire every time. If you put the bird/dummy all the way in the bottom of the pouch the arm does not hit the primer hard enough all of the time. Juat some fyi for you folks.