Ok I realize I wasn't clear enough on the game mechanic involved here, it's not so well known. What this machine does is:
step 1: produce a lot of cobblestone
step 2: ignite a tnt
step 3: in the same game tick the tnt blast, push the cobblestone toward it.
This way cobblestone is turned to block 36 type cobblestone block, which has no blast resistance and 100% drop rate. You get more than 3 stacks of cobblestone per TNT, awesome compared to blasting a TNT inside a cobblestone cube where you'll get something lame like 16 items. The same principle works for a wood farm for instance.
I'm making a very simple (but slower) contraption to show you.