This is a 50 Round 5.56 NATO / .223 Remington ammo box. It has a locking sliding cover. I like to slide the cover back to reveal 5 rounds and dump the out in 5 round increments. It was designed to have the bullet side facing up. It can work work with the primer facing up if you wanted.

Please note: The middle tray that holds the round snaps in mid way down inside the box using two detents. To install just press the middle tray down until it locks into place. The round bosses should face down with the flat side on the top.

Check out my other ammo boxes for similar designs. If you are looking for another caliber, just let me know via a comment. I can usually quickly make one.