Step 1 - Put all gear you want duped on an alt account.
2 - Give account to a friend and have them favorite a server.
3 - Have them log in to the server while you prepare to sign in to the account.
4 - They tell you when their timer hits 5 seconds then you log in and get into the server as fast as possible.
5 - As soon as they get on the server they drop all gear on their body as fast as possible.
6 - They get kicked and you spawn in fully geared with the kit they just dropped still there.
7 - You log out of the server , then the account. Rinse and repeat for as many dupes as you want.

The player with the alt account was using an SSD and an Xbox One X. The other player was using an Xbox One X and the game is installed on the internal harddrive.