I sure hate to tell the gunsmith that what he has been doing for so long doesn't really work. As to the nitric acid, there is an ammonium nitrate plant built in WWII near the same town that has a huge nitric acid plant. Nitric acid is not hard to come by.
How about pure bromine to kill moles. Just a few drops in their tunnel and they are all gone. There are three bromine plants in the area.
By the way, I don't drill and tap anything.