In Dealing with a possibly gun shy dog I used 410 chamber mates through a 16 and ensured I did not shot directly over the dog. The sound was greatly reduced and the dog focused on the flushing pigeon and not the gun.
Actually silencing a SxS does not interest me
I have had two hunting dogs. A Weimaraner and presently a 1 1/2 year old Springer. Last summer, I broke my Springer by taking her out to the shooting club and held her behind the trap pad on a leash, during a tournament. The results were the same last summer as with the Weimaraner- 15 years ago......... First time-pretty scared. Especially with all the people walking past her. Second time still jumpy. Third and fourth times, wanted to romp and play more with the shooters than paying attention to the shooting, because everyone wanted to play with her. It never took long to get a dog of mine used to gun noise. Now it doesn't bother her at all to take her out to the club and tie her up while I shoot a couple rounds of trap. I worry more about the fleas and ticks in the area. It doesn't take long for them to get used to it. Good luck.
I've gun broke my dogs by using live birds and a buddy shooting a .410. With planted bird, I would allow the dog to sense the bird while on along lead. Once bird sensed and pointed (Brittanys as other pointing dogs instinctively do) I would flush the bird--as soon as flushed, a buddy with a .410 would shoot a 100 yards away. Next bird, flush and shot at 75, sequence repeated closer until standing behind us with the gun. Using same technique, some prefer the dog to chase bird before shooting. I have success with the "flush" and contemporaneous shot, but only after letting dogs experience planted birds previously without shooting. Every now and then I'll hear of a knucklehead shooting a 12 ga. over a dog's head while dove hunting and wonder why the dog ran away doomed to being gun
shy. Two weeks before gun training, I'd shoot a cap pistol while feeding the dogs working closer and closer. Plan was if I saw a flinch, I'd back away and work in, but don't recall seeing adverse reactions and having to back up and start over. Gil