Buy a book and read it very carefully. Why the hell do you want it catching a dummy in mid air?? And only 2 and 1/2 you should have started this 2 years ago.
I think you need to speak to someone who trains dogs for some help if you are serious about training him. He isn't deaf it's called I'm not close enough for a bollocking so I'll ignore you, anyway good luck with him.
I would say your dog like all the others on here that have problems need more work. Just because a dog hasnt heard a gun go off in a couple of months wont change how it reacts to the sound of a gun.
Only problem with semi auto's you have to clean them to keep them working correctly. I think Ive cleaned my 452 once since having it and it works every time.
It really all depends on the land. Has the farm got set a side land and/or conservation headlands? It would be possible just needs carefull management.
Why not make a collar to work with b&f barryvox etc. Or just a simple version with a number display like the terrier boxes. Also a collar that doesnt catch on nets but thats near on impossible.