Check out my K'nex Breaking Sniper too!
It's the turret for KillerK's gun! The gun is easy enough to build from his slideshow but a lot of people struggled with the turret, so here it is! The TR36 turret is built in the same way, but twice as big!
I have all the necessary permissions. Credit to BakenBitz for the 18 shot concept and KillerK for the design.