If your dog goes bonkers at the SIGHT of a gun, then you can be 100% sure that someone has abused the animal with a real or toy gun before, even if secretly. Do you have children in the house? Neighbor kids ever have access to the dog? Kids, with toy guns, can be cruel to dogs, thinking it a lot of fun to shoot at them and watch them become frightened. Best way to ruin a dog is to allow a kid to shoot it with some nerf projectile, or something similar. Really hard to fix that problem. Some people lay a gun down next to the food bowl each time it's time for the dog to eat. Try this for a while. If the dog won't go near it, place some other object about the same size next to it every time it's feeding time. After a while, try the gun again. After a few dozen repeats with no apparent fear, touch the gun while the dog is eating for a few dozen repetitions, then hold it while sitting near the dog as he is eating. If your dog has a good appetite, this method might work well. The gun will soon become associated with the pleasant sensations the dog associates with eating.