I designed a 9mm bullet box which holds 50 rounds.

The top slides on and is hold by grooves in 5 positions.

That way it locks in place to reveal 10 bullets at a time.

Easiest way to open it is by pushing in the middle of the lid, because that way, the “locking pins” disengage.

This is the version vor 9mm Para.

I also have a version for 9mm blanks P.A.K