So, sure, go after him for the buildings if they didn’t have a permit to build, since that’s a potential safety hazard you don’t need when handling firearms.
However, if the neighbors of the property came in after the property was made a gun range, then I have zero sympathy for them in terms of the noise since, to me, it’s no different than building a house near an industrial factor or a railroad or a highway: It was already there, the noise would’ve been expected, and if you chose to do it anyway, well, that’s on you, not on the range/factory/railroad/highway/whatever.
I mean, yes, I agree, but I’m curious as to what exactly the structures are, too. If we’re talking about an average “shoot house” type range, where it’s just a bunch of walls built to resemble a building, beefed up to properly stop and contain bullets, or some other similar “structure”, sure, going after him over the lack of a permit for it is legal, but seems like it’s being done more as a means of nickel and diming him with every technicality because new neighbors are NIMBYs than because there’s a legitimate issue