The GVAC system from Gemtech. Significantly reduce the amount of gas blowback you'll experience wwhen shooting suppressed with its patented design. The re-imagined barrel profile, enhanced bolt carrier profile, enhanced bolt carrier group, and ETM muzzle device maximize peformance so nothing holds you back. Redefine suppressed shooting with the GVAC system. UPPER RECEIVER - Mil-Spec with Indexing Marks and M4 Feed Ramps. 7075-T6 Aluminum, Type III Hard Coat Anodized BARREL - 4150CMV Steel, Stress Relieved, Armornite Treated, 1:8 Twist, 5R Rifled, GVAC Profile, Nickle Boron Coated barrel Extension, 1/2X28 TPI Muzzle Threads GAS SYSTEM - Pinned Low-Pro GVAC Gas Block, 4140CM Steel, Mid-Length GVAC, Direct-Impingement MUZZLE DEVICE - Gemtech ETM Flash Hider, 4140CM Steel BOLT CARRIER GROUP - Carpenter 158 steel bolt, 8620 Steel Carrier, Mil-Spec MP Tested, Mag-Phos Finish, Chrome Lined, Properly staked Gas Key, Enhanced reliability bolt carrier and chrome firing pin. HANDGUARD - 15 Midwest Industries Combat M-LOK Free-Float Seven Sided M-LOK hand guard. Continuous MIL-STD 1913 Picatinny Top Rail, Integrated QD sling sockets. Machined from 6061-T6 Aluminum, and Type III Hard Coat Anodized.