You will need:
-Metronome
-Reconstructor/Healing Gun
-Humans

Firstly u will pause the game, spawn a metronome and a reconstructor and disable heat damage.
Then u shall spawn in ~30 humans in one place then u will freeze them, after that u will move the heads so u can't see the bodies.

Now u will set the metronome to 2,5Hz and connect it to the reconstructor with a propagation wire and point the reconstructor at their heads, and now u copy the contraption until the FPS fall down to 15-20 (For me its a 4x2 block of heads)

Now u have a contraption about twice as efficient as my old one! (250 kills per tick)

Have fun getting the achievment!