VK-1 Complete uppers features: Bolt Carrier Group – Precision machined one-piece patented bolt carrier with correct timing, revised cam path, finished in thin, dense chrome. Patented enhanced cam path for consistent lock up, shot after shot. Match performance right out of the gate. Enhanced Upper Rail – 15 slot upper receiver rail creates a truly continuous 12 o’clock Picatinny mount, optimizing available accessory real estate and reducing the overall weight of the forged upper receiver. Thermal Fit Receiver – VK-1 upper receivers utilize a thermal fit to provide the highest level of accuracy potential while eliminating any heat-related POI shift. VK-1 Piston System – Features our patented low-profile piston system, specifically tuned to maximize reliability in all conditions with the smallest footprint possible.