The duplication glitch is very simple really all you have to do is place the block or item in a dispenser then have your friend destroy the dispenser and the block(s) you just placed in there should turn to 64, place them in your inventory NOT your hotbar, then go to a chest and place the block(s) of 64 in there MANUALLY, this mean do not use the 'Y' transfer a.k.a the quick move, now whenever you want to duplicate you simply pick up the block of 64 and hold 'x' on a slot in your inventory or in the chest and if you did it in the chest just place the block in your inventory and your done and to do this by yourself get your dispenser and dig 2 blocks under it and place TNT then quickly hit the TNT and go quickly go back in the dispenser menu. Note: I do not take credit for the following video it is just an easier way to show the community but i do take credit for all the text written in this post, the duplication is not mine i was just showing you in a hopefully clear tutorial.