When I feel the pup has chased good and does not balk at flapping wings etc. I take a clip wing pigeon, and hup the dog in front of me. I have a gunner with a low base or a popper shell, (Light load) down wind always, about 60 yards away. I throw the bird as far and high as I can, with the wind. It can flap out quite a ways before coming down. If the bird some how heads toward the gun, do it over. The pup will and must be in chase, if not I don't shoot. Just before the pup reaches the bird, say a few feet. I raise my hand and the gunner fires away from the dog. He only shoots if I raise my hand. That way if I see something I don't like he wont shoot. 99 % of the time it is fine and the pup will pay no mind to the gun. I repeat this several times and gradually have the gun moved in closer over several "different" sessions say 3 or 4 tosses per session. After worked into reasonable gun range, I plant flyer's for the dog, and run them into the wind 1/4ing. (always in to the wind). They will flush and chase, and then let it ride a ways before shooting. Never blast it right in front of the dog short. If it ends up too close to the dog and the gun, just do another and let it fly away. It always works well and the praise follows. I keep using light loads until the dog is doing it with good confidence, a few weeks. Then a bit more shell and some smaller hen pheasants. Reason being hens, is because roosters, right off the bat, can hurt a dog. Have you ever been tore open by a rooster claw? Well a dogs face and eyes, lips , nose etc. can get the same thing, They do the death flop from hell offten and can scrape a pups face. If it is one of there first experiences dealing with live birds, it can make the flush poor, or make them not want to pick up a bird ever again. It may not happen, but can and does. taking this slower approach is full proof 99.9999999% of the time and there will not be any issues. Dogs are not born gun shy, they are made that way by human error. My self, I am lucky to have never had a gun shy dog using this approach,and it useualy results in great flushes or quick pick ups. I have seen plenty that were rushed, that ended up gun shy. Hope this helped.