Muzzle device designed to port excess air but at a slower rate, this reduces the overpressure affecting dart flight path, whilst simultaneously acting as a barrel extension to allow blasters to hit slightly higher that it otherwise would. This concept only works assuming your set-up is under barreled. 

10 bearings per row provides a twist with consistent shot placement. Not sure what's the maximum FPS recommended for this but tested up to 200fps at the given moment. Will update findings