Our take: JBU's inner barrels are made from high tensile, aircraft grade aluminum, using precision CNC machining. These JBU 6.01mm tight bore inner barrels provide maximum accuracy and increased FPS in any AEG. Because these barrels are precision crafted, only high quality, precision grade BBs should be used with this inner barrel. The JBU Tight Bore 6.01mm barrel should fit in most AEGs, and should be compatible with most hop up systems. Professional installation is recommended for anyone unfamiliar with installing a new inner barrel. 

The super slick performance finish strengthens and protects the barrel, while reducing friction (conserves velocity & back spin).  This 300mm inner barrel is for M1A1 Thompson, M733 and M4A1 Commando metal gearbox AEGs.

Precision manufactured to ensure durability and high quality.

Note:  Ready to use right out of the box, though professional installation is recommended/may be required.  Please use only ultra high-quality precision seamless BBs in your gun after installing this barrel, as inferior grade BBs (i.e. BBs from sporting goods stores) WILL jam inside this barrel.