Thank you! A great tip with the cartridge neck. It still looks like my camera is way too far focused. To get an in-focus image, I had to unscrew the mirror completely, and move it 1/2" away from the camera...It’s fixed focus, so you adjust the distance from the mirror. Try putting it inside the neck of a fired case, which will be close enough to the bore diameter for you to adjust it.
Or not... It might just went hyper-focal at this distance. Just how precise this adjustment have to be? A full rotation? 1/2? 1/4?