Now in stock at WGC Shop are the A Plus Airsoft 6.08 Nickel Coated Copper Rectifier Inner Barrels for the GHK Gas Blowbacks and available in different sizes... "Pressure-balancing design, relieves pressure difference between atmosphere and inner barrel, minimizing turbulent flow's effect on BBs. These have 6.08mm Inner Diameters, made of Copper Material, and 60 Degree Chamber Packing included.