I had a silimar problem with my lab. Since your has had experiance with it and is scared already, you should try to put him in a dog crate wil you shoot. It will prevent him panicing and trying to run and choking on his collar. It may help to imprint that it is something to be scared over. Put him in a crate and stand in front of it where he can see you. Don't pay any attention to him while you are shooting. Over time, if you don't make a big deal about the noise he will probaly just go to sleep. Start with some thing small and work up toa bigger calaber. next time you go out, put him on leash. hold onto it don't tie it up to any thing. Have a friend start shooting. Just walk your dog around the area. Pretend that nothing is wrong or different give him treats occationaly. The most important thing is not to act like you even hear the noise.