Pro2a Tactical has the latest 6mm ARC NR Side Charging Uppers on the market. The 6mm ARC (Advanced Rifle Cartridge) developed by Hornady, was voted AR-15 caliber of the year 2020 and is becoming an extremely popular hunting round. The 6mm ARC's high ballistic coefficient and high sectional density offers less drag and less energy loss at greater distances. All of Pro2A Tactical 6mm ARC NR Side Charging Uppers are made here in the USA using the highest quality materials and backed by our limited lifetime warranty.