It was mentioned that Lucas' cabin is in Wisconsin. However, when he is driving to the cabin, the narration has him traveling I-35. That is a north-south part of the interstate system that does not cross into Wisconsin at any point so he would have to take I-35 to another local highway to cross into Wisconsin.
Lucas asks Marcy to have ballistics tests done on a cartridge that hasn't been fired. There will be no marks from grooves, no firing pin mark and no extractor marks. All they should be able to do is possibly determine the brand.