How To Open Or Use Purple Lockboxes

Purple is always for rare loot in these kinds of games so im annoyed u can't figure out how to open them. I've killed 2 larger enemies and both times they have dropped a purple lockbox. How do I open these lockboxes to get the loot?

These purple lockboxes are just ammo containers for your heavy or special weapon. They arent actually an indication of any legendary or rare weapon type.