Free Floating Carbon Fibre Outer Barrel for M4 style AEGs with dual inner barrel stabilization in the front and the rear. Choose an inner barrel in length at least equivalent to that of the outer barrel for maximum stabilizing effect. HopUp Unit guides are ideal for XFORCE HopUp Chamber (also compatible with other HopUps, e.g., MaxxModel) to provide reliable and stable centering of the HopUp Unit.