This is a small collection holder for spent (or unspent) rounds.

This particular set is for NATO Small Arms: https://www.wikiwand.com/en/NATO_cartridge

It's arranged from size of base, but the height model has it based on height.

Note: The display photo was printed on fast, which ruined the text. The modeled uploaded here has larger, bold text and is meant to be printed on Normal.

If you want to print the casings: 50 Cal - https://www.thingiverse.com/thing:3526400 7.62 - https://www.thingiverse.com/thing:4937154 5.56 - https://www.thingiverse.com/thing:3882735?part=0254ee83-fbc1-4402-a4b1-774211a97f1e 9mm - https://www.thingiverse.com/thing:4432631/files 5.7mm - https://social.thangs.com/m/686504