Holder for my previous model - https://www.printables.com/model/237424-12-gauge-shotgun-shell-container
It's inspired by first Doom game where it held 4pcs of shells.
If printed on 100% scale its little looser but shells will stay in. You can scale it little down (maybe to 97-95%) to make tighter fit.
The author marked this model as their own original creation.