Using Inventory & Vending Machine Screens in Borderlands 2 (Back to screenshot); Equipped Weapon Slot #2 — Available to be filled with a favorite weapon. I apparently missed out on getting the first weapon slot SDU. I was playing co-op with a friend, and we got up to that point, took a break, then the. I have two "locked" weapon slots. How can I unlock them? locked They're obtained in parts of the main story; one in the early Sanctuary.