I'm quite new to modeling, but I wanted to try my hand at organizing my gun safe. 

These 5 shell caddies are designed to mount to the wall of a safe with magnets or velcro. The backs print flat, but I CA glued magnet plates to the back of mine and they hold 5x 3in slugs quite well regardless of their weight! Shells fit snugly but loose enough to pull out smoothly, with the brass end sticking up enough to grab. 

The 3mf file should be properly oriented on the plate, but if you're printing from the STL I recommend orienting the model flat on it's top surface with the peak of the wedge pointing up.