I agree with Sabine, ignoring it will not help, and a BC probably will turn it into a major neurosis if it's not addressed. I would use a really happy voice and say something like "there's the bang!" and feed him several awesome treats EVERY TIME the noise sounds. I did this with a shy Sheltie who was terrified of the sound of the teeter in agility class when other dogs were running the course. She would try to bolt from the building. Once we made the bang a huge payout for her, she came to accept it and even years later, would automatically turn her head for her treat whenever the teeter fell. I think the happy, stress-free tone is important, like you and Ranger are sharing a joke, not like you're annoyed by the noise.
Get cheese or liverwurst, something SO GOOD that just the smell will be delish to him. Make it a soft treat so he doesn't have to chew, or he'll spit it out.