The barrel itself is a two piece, two step screw together masterpiece. The first 5 inches is what we call the control bore. (this is the distance that most experts agree is the most critical in a barrel) The second screw-in piece is called the universal tip. This tip is honed to a 0.700 bore diameter, thus allowing the blast of air to completely surround the ball, reshaping the ball spherical again.
The Custom Products Pro-Barrel System is newer, so it should be commonly available, both new and used.
I bought the base kit then later bought the 12 inch and then 14 inch tip for my autococker and switch it back and forth on my sniper II. I gotta tell you, it's a good barrell system. It quiets your shots and is accurate. And the obvious benefit is the ability to switch bore sizes and tip lengths. It also comes in a variety of colors for the tips.
The bore section of the barrel scratches pretty easy. It also doesn't come with barrel o-rings which are defintely a must.