As normally I think, Alt+F4 tells the program to end, and if the program doesn't stop, another Alt+F4 directly stops it. Or that's actually a bug in Java or mc?

p.s. I almost never dup successfully, so I wrote a script that press ESC, wait for a moment, and kill Java. When playing Escape the Wool Complex(requires to collect enough dye to continue), the waiting timing varies. 100ms is sometimes too long(when re-get-in no item in the world), sometimes too short(when re-got-in no item in the backpack)

How to dupe successfully: Throw items onto ground, s+q, relog, collect items, Alt+F4 (Should instantly close minecraft after one press), reload minecraft (easiest if the launcher is set to automatically pop up), enter world, and boom, duped items.]

Now, duping isn't as simple, it's a fickle process. The timing of the Alt+F4 is precise. Too early, and the items won't be duped, and instead you'll appear just before the dupe, with the items on the ground, and not in your inventory. Too late, and you'll appear where the items were and they'll be in your inventory, but they won't be duped.

The reason this happens is because of various types of lag. Duping in the Nether or End has a lower chance of working due to a smaller time window (Additionally in certain versions duping in the end can clone the Ender Dragon or render collecting a certain Advancement in 1.12 unobtainable). Duping isn't an exact science, you just have to get a feel for it.

Also, sounds like you're pressing Esc before doing the Alt+F4? Don't do that, pressing Esc saves certain parts of the world I think, and also can change the timing and affect lag etc.

If I directly Alt+F4, I almost never succeeded. ESC is before the taskkill, and the delay is also set. Or if the render distance is large enough, the current part would be later to write, and it gets easier to dup? Or when recording videos the harddisk is busier and duping is easier or harder? Is it possible that dup writes level.dat but not into the stat file? If so timer is not accurate

Pressing Alt+F4 and pressing Exit-Java hotbar, the delay till minecraft close is clear different

When Render distance is 64, ESC and soon Alt+F4 dupped successfully

Seems render really differ. Usually when I play minecraft, I use a small render to make it not so laggy(as said before, a $300 with-screen computer in 2014), and maybe it leads to the failure

With Render 16, Superflat y=200 I can do 1->6 dup, but y=3 can't do any

When playing Default World Render=16, even waiting for 5s and Alt+F4, relogging in no item in the inventory; ESC+Alt+F4 always too slow; Esc Taskkill is possible

[11:27:52] [Server thread/INFO]: getchar joined the game [11:27:54] [Server thread/WARN]: Keeping entity minecraft:chicken that already exists with UUID abe6ffe9-1384-47d3-a82c-7e0e307055ac [11:27:54] [Server thread/WARN]: Can't keep up! Did the system time change, or is the server overloaded? Running 2203ms behind, skipping 44 tick(s) [11:27:56] [Server thread/INFO]: Saving and pausing game... [11:27:56] [Server thread/INFO]: Saving chunks for level 'Duplicate'/overworld

If I use java.exe instead of javaw.exe, and close the console instead of minecraft, dup success in Default Render 16

When killing wither skeleton, setting the environment so that Alt+F4 can be early. For fail tries, it don't count the time? (I guess IGT timer can only read that) When unlucky, it can save a few minutes

The duping glitch is, well, a glitch. It can differ for everyone depending on hardware and performance of your computer because it's an unintended result produced by some defect in either the program being run or the environment it runs in. I could, in theory, even be impossible to do for some people.

With script duplicate can be 10x per second or something, and without script it's also possible, but the success rate would be tiny

Scripts are discouraged, and can sometimes be counted as inputmods that give an advantage (keep in mind the rules disallow all mods that give advantage, including system mods, input mods, java VM mods, hardware mods, as well as, of course, minecraft mods). So if a run you submit has obvious use of scripts doing stuff a human would not be able to, it will be rejected.

Since I made my own computer does that count as a hardware mod? Do I need to buy a microsoft-approved computer?

Here only talking about possibility, and using scripts is only to make the possibility clear(like TAS which make things with small possibility happen). That shouldn't be allowed here, but if the rate is high, there's also not much difference between script and direct doit. Tasing may allow that since it allows possible, but it's not what here care Same to April, not knowing what hardware mod mean

I guess hardwaer mod does not really apply to a PC game given the wide range of available hardware options for a computer. My bad on that. I typed that on reflex thinking of console video games.

Ok there is hardware mod. E.g. you replaced the PC timer with a slower one Any other?

Great explanation in 2nd post.

Some info say vanilla 2s and optifine 200s(written as 3min). And I tested o optifine both 2s and 200s lead to save per 45s. Don't know about them