Screw the snare. To create a spooky soundtrack suited to the sinister world of sci-fi hitman flick Looper, composer Nathan Johnson designed a virtual drum kit featuring the clicks of a prop pistol.

“It quickly became clear that our starting point was going to be drums, but not drums as we know them,” says Johnson in the exclusive clip embedded above.

Looper’s time-travel story revolves around two versions of the same killer, played by Joseph Gordon-Levitt and Bruce Willis. Johnson underscored the movie’s violent theme on a subliminal level by borrowing a handgun handled by actor Noah Segan.

“We recorded all the little sounds that a gun makes and once we had these, we swapped them in for … kick drum, snare drum, hi-hat,” Johnson says. “Eventually we put them all together for a completely customized, playable drum set.”

The strange instrumentation didn’t stop with the pistol. Johnson and percussionist Chris Mears used a Los Angeles parking garage with “amazing natural reverb” as an informal recording studio to capture audio of slamming car doors as the foundation for kettle drums. To evoke the atmosphere of a wormhole-infected universe that’s collapsing upon itself, they trawled hardware stores for chunks of plastic and metal.

“Looper is a world falling apart,” Johnson said.

Looper, directed by Rian Johnson, debuts Sept. 6 at the Toronto International Film Festival, followed by a wide release Sept. 28.