Locations of weapon crates in Headstone Mine.
Location 1: Building opposite MK2 gun
After fighting first group of bandits, a side route has to be taken due to a locked gate. Continuing straight ahead inside the second house. It is inn direct line of sight with an Mulciber Mk2 gun.
Location 2: Near Sledge room's sidedoor
Just outside the side door that gets opened once Sledge is defeated is another house with a red chest inside. It can be accessed before or after Sledge is defeated.
Location 3: Plain sight
Near the lift that takes Vault Hunters to confront Sledge. Can't be missed.