No slime TNT duper cobblestone farm

A compact cobblestone farm run by a TNT duper. Water and lava make the cobblestone, duped TNT blows it up, and hoppers under the farm drop it into chests, so you AFK at the storage. It needs no slime blocks or sticky pistons. Builders feed the output into a super smelter for stone. TNT duping is a bug: the farm works in single player and only on servers that allow it. Switch it off before you leave the area, or the TNT blows the farm up. The storage is basic, the creator says he never designed a good one.

• Switch the farm off before you leave its chunks. Left running, the TNT blows up the duper and the farm. Top comment on the video, the creator confirms it.
• On a server, allow TNT duping first: Paper blocks it by default, set allow-piston-duplication to true in its config. Many builders report it, the creator says servers patch the glitch.
• If only the last TNT breaks cobblestone, the duper fires before the cobble regrows. Set the locked repeater to 3 or 4 ticks or add a repeater to the clock. Several builders fixed it so, the creator agrees.
• If the TNT does not dupe, check each repeater delay, use a note block not a jukebox, and face the first observer as at 6:44. The creator says normal pistons; a fix with 34 likes uses a sticky first piston.
• Waterlog the slab and the stairs as in the video. Dry, the TNT destroys them; waterlogged, any material holds. The creator repeats this in several replies.
• Keep players, villagers and pets more than two blocks outside the outer glass while it runs, the blasts reach that far. Comment with 46 likes.