The specific boxes of Blazer ammunition I have include plastic inserts that measure 138.6mm x 69mm. These fit nicely inside the case as shown, and just make it look a lot nicer than having cardboard boxes at the range. Models are in correct orientation for printing, which should be pretty obvious anyways.
Print to your preferred density and materials. I printed in Overture Matte Black with some generic white PLA for the “9MM” label.
The author remixed this model.