50 round 9MM ammo box with tab secured lid (probably not range bag secure). Has a slot in the front for load data sheet or simple identifier tags. Stackable with more pistol ammo storage boxes or rifle ammo storage box with either on top.

Revision 1: Added a 3d printed tag to the 3mf. You can use the Make My Sign tool in MakerLab to make this (I didn't because I didn't think about it). Tag is 43.6 mm wide x 15.6 mm tall with a .6 mm thickness.