This isn't apples to apples, but for what it's worth, I got help from a pro trainer because my pup was very shy about gun shots. He had done ok at first, but then started to get increasingly scared. The trainer had me start from the very beginning and work up slowly. The first step was just clapping. I would clap at random times when we'd be out walking. Often, I would try to surprise him with the clap. We did that for about a month. Then he had me get a cap gun (like the kids version). I started carrying it around on all of our walks and I would just fire a cap randomly. I did that for at least a month, until there was simply no reaction. Then I went up to 209 primers (I had my brother load me up a bunch of empty shotgun shells with just a primer since I don't have a blank gun). At that point, we actually started hunting a bit and I would fire a 209 if we flushed a bird. Eventually, we went up to light 20 gauge loads, but I would only fire them when the dog was not right next to me and I would point it away from him. All of these transitions were a bit diffuse too, so I would clap sometimes when we moved on to caps, etc. And any sign of being startled, or afraid and we would dial back a bit. Eventually, we just transitioned right into regular hunting, but it was months and months of doing this stuff all the time and it was worth it. It's an absolute non-issue now. He just associates gun shots with bird hunting and bird hunting is his favorite thing in the world.