There's two ways that you can drop weapons in Jupiter Hell. The first is by heading into your inventory screen, by pressing the Start button on controller, or I on a keyboard. Press left or right on the D-Pad or Arrow Keys on the inventory screen until you see the Equipment menu.
Highlight the Weapon Slot you want to drop by pressing up and down on D-pad or keyboard, and then all you need to do is press Y or D. Your weapon in that slot will be instantly dropped. With a slot free, you can then pick up another weapon to take its place.
The second way to drop a weapon is by having all three weapon slots full and exchanging one for a new one. Suppose you come across a new weapon and want to add it to your collection. Upon pick up, your current weapon will be automatically dropped in exchange for this new weapon.
This is the quickest way to drop a weapon, but you have to be extremely mindful of the weapon you have equipped. No one wants to exchange their best weapon by accident.
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