I have a small arsenal of C02 and spring-piston BB and pellet guns. I store all of them in a single rifle case. However, I didn't have a good way to store 12 gram CO2 cartridges in the case without them rolling around. This design lets you easily store 5 or 10 cartridges in a flat package.
The 10-cartridge model is suitable for printing on any printer with a bed length of 220-230mm or more. If you have a smaller printer, you'll want to go with the 5 cartridge model instead.
The models print fine without supports. I'm using eSun Pet-G at 20% infill, and the cases printed solidly enough.