This is the sort of thing that to me at least, is known for whatever reasons when you are younger, only to find out why many years later, thanks to the internet.
Hunting dogs don't flinch, cower, freak out or otherwise react adversely when a 12 gauge shotgun goes off. To the contrary, to them this means it's time for fun in the field. Years ago when I was real young I had a buddy who's father was into hunting, reloading, the whole deal, and asked him why this is.
Dogs are very receptive to new things when young, and when exposed to these things when young see them as normal, not out of place. For a pup that is being trained for hunting this means being exposed to all the things involved with hunting, including the loud report from firearms. They grow up with this being normal, and live their life accustomed to this.
A few years later, being a slightly older kid with my parent's picking up a poodle pup I remembered this. I didn't want her to be afraid of my buddies & I blowing off the usual illegal fireworks, so I exposed her to them. Kicking back in the yard with the pup, tossing the occasional small firecracker, working up over time to bigger things. Independence Day sounds like live fire military maneuvers around here, the dog was never bothered by any of this. There is no controlling it around here, the street has a fog of smoke wherever you go.
Years later, my folks got a beagle mix pup, same routine, same results. Learning from this I expose all my dogs to fireworks, power tools, loud guitar playing, you name it, they could care less. I had a westie that would intentionally go into the garage when I was playing bass, there were mice, the loud sound covered the noise from his tags. If I stopped playing he would stop dead, smart little dog.
It all comes down to exposure at a young age. From the sounds of it Ludwig you are in an area with more wildlife than I have here. My guys have never seen a goat, horse, sheep, chicken, any of that, and would probably go nuts over it. What they have seen, about 20 feet outside the back fence, is a street and high school with all the busyness associated with that. Fire trucks & ambulances flying by don't get noticed, no vehicles really do, this includes some really nice, fast hot rodded cars. Street resurfacing equipment got looked at, then ignored. The marching band gets ignored. Large wild crowds of kids on football night get ignored. They get to see parades on occasion. Chewing on a stick is more interesting to them.
Researching this about 10 years ago, thanks to the internet, there is a window of opportunity with dogs that closes at about 5 months of age. Before this, expose them to anything & everything, always something new, different, or odd. Funny how there are things you know work when you are younger, to find out why many years later. Feed them out of different bowls, expose them to as many people as possible, explore different situations & surroundings, the only limit is your imagination & general safety.
The only one this didn’t work with, due to an odd situation, out of 8 or so dogs, was my yorkie. It worked out fine at first, nothing loud or out of placed bothered him, until he was almost 2 years old. One night, during a thunderstorm, lightening hit the chimney of the apartment building behind ours, in the middle of the night. We were living on the top floor, asleep, it knocked all three of us out of bed. We were all shook, but he took it the worst, still shaking in the morning. A trip to the vet to make sure there was no injury, I’m serious when it knocked us out of bed.
After that anything loud, he would go hide someplace, usually in a corner by a couch, never on a top floor when we moved into a house. If it was real loud he would do the shake & pant routine. We tried the gradual acclimation trick, where you start a recording, very softly, of whatever bothers the dog, very gradually over many days turning up the volume. Many tries, several months, when it hit a certain volume he would go hide. We did get tranquilizers from the vet, but really didn’t want to use them unless we really had to. There were only a few times a year when we needed to, really bad storms, or firework holidays. He’s the reason guitar gear stayed in the garage.
lol theres about 4 fiework shows with in a mile radius of my house, so its best to find the highest viewin point and look over them all 
