WORKS ALL PLATFORMS
Step 1: Have a friend invite you to a game. Whoever will be receiving the items MUST be host.
Step 2: Set up a trade and select the weapons you want to duplicate.
Step 3: Confirm the trade with your friend and simply close your application when the timer says 1.
Your friend will now have the weapons and when you reload your game you should as well. The timing is super easy on this one, it works every time. I also have some modded items if you watched the video that I am willing to dupe with anyone, Xbox - OiAvogadro.