Modify Hybrid 6.01mm Precision Inner Barrel 363 mm for M4A1

– Hybrid Stainless Steel plus Aluminum Construction – 6.01mm Inner Diameter – O-Ring guidance to reduce barrel vibration – 3 Grooves and 2 O-Rings for outer diameter adjustments from 8.6mm to 9.2mm to fit different outer barrels – Proprietary 3-Ring Chamber Packing for better air seal