I wouldn't give up on him just yet. How old is this dog? Perhaps you're pushing him too soon?

tailcrackin (Jonsey) has some good advice on introducing the gun. But you have to get your dog excited about birds. A suggestion, get asmall bird (chukar or pigeon)and anchor it's feet by tying a 10' or so cord to it. It will try flying around and the dog will see it as a plaything. Let your dog play with it. You will loose the bird but you'll help the dog.

Some dogs just don't have it.