@MiraSTRU

as of may 8th 2025 it still works. (v 1.21.5) The reason why this works is that barrels / chests have autosave. It is YOUR autosave, so this will work on any single player, doesn't matter if hardcore, or creative. It wont work on servers because you don't save server- server is saving itself -  you just log in and log off from it. It MIGHT work when you're only one there - try it.

And for those that are saying it doesn't work in SP, here are some mistakes that you might be doing:
1. open barrel and put everything in 
2. don't go to menu, dont click away from barrel menu - you don't want barrel to close.
3. when you put everything in, count to 5 or so, if you close the game too soon  - it wont duplicate. It needs time, important thing is to not click away from barrel menu (dont close the barrel)
4. dont hit windows key on keyboards to get to task manager. Use control + esp to get there. This is a windows emergency combo lol 
5. then close minecraft in task manager
6. open and log back in
7. you will have duplicated ithems

and now important: SAVE IT. Save it WITH the duplicated ithems again, proper save, and THEN do the glitch again - if you need more copies. That save between glitching is important

And note: sometimes ithems can disappear with this. So make backup before you will be doing this. Also: dont dupe all recourses: lets say u have two diamonds. Don’t dupe both of them at the same time. Dupe one- .. then u have tree. Put the original one back in save chest, and dupe that third one. Then u have four. And then dupe that 3th and 4th, leaving your originals always in save chest (not barrel). So in case those dupes will magically disappear you wont lose 4 diamonds but just 2, and you still have your 2 that u had. Its like gambling, put there only things youre willing to lose.

@MrBroontlay

instructions unclear: my items are gone

Update: works now for me on 1.21.5

@CheeseMeat_

A warning that all of you should know: Before duping, put everything you DONT want to dupe into a separate chest. Including armor and anything in your off-hand. Then save and quit like normally. Once you rejoin, then you can dupe. This will prevent you from making dupes of stuff you don't want or if you butcher it and you lose your items.

@Doomeditz69

Can confirm this works in 1.21.1 java on normal launcher and feather

@kundanjha739

I am.......
...

Steve

@anojjayangana1241

It happened to me accidentally due to a powercut

@Expectation69

for some reason my armor glitched out of existance so I had to make a new one this video helped me do that thanks dude

@ohohohhesacthequeen

Instructions unclear, items gone

@selkielore

this is the only duping glitch that works for me

@TeighanKochOfficial

Does this not work on realms?

@MeLikeAlmondButter

I don't see how it would work cuz technically the items are already in the barrel

@GigaSteveplayz

Happened the same with me with a furnace and my iron got duplicated

@chose_jesus

I tried to duplicate netherite but I just duplicated all my beds and my amour?

@BonBon01285

it only works for single player

@tylorpitman7133

All my items disappeared

@Pranasvirkutis

works in 1.21.5

@mrtiger6032

This works in single player but not in multiplayer servers can you make a video for this😢

@Creatineee

does it work in realms i’ve tried it and it doesn’t but idk if i did it right

@kae299

On iPad?

@CarEnthusiastt-x4p

ummm my furnaces are broken i cant cook anyhting other than the stuff that was in them