Despite the understandable misconception of many new to Airsoft, a BB being fired does not (or at least should not anyway) touch the inside of the inner barrel. The air / gas pressure behind a pellet pushes the back of the pellet hard but also slips around the pellet escaping forward through the gap between the inner diameter of the inner barrel and the outer diameter of the BB pellet. This tight flow of air around the pellet prevents it from touching the sides thus a pellet being fired is actually riding down on a cushion of air for minimum friction and maximum acceleration.
A tightbore barrel reduces the inner diameter of the barrel in an attempt to reduce the space between barrel and pellet resulting in an even tighter air flow. A good quality cylinder strives for a minimum amount of superfluous air flow and a consistent delivery of pneumatic power on every cycle.
The Raven (PDI) line of products has a very meticulous manufacturing and inspecting process which results in parts with unparalleled quality and performance.
This set contains only the cylinder and cylinder head.