This AR-STONER pistol barrel features a 5.56x45mm NATO chamber for full compatibility with surplus mil-spec ammunition or commercial 223 Remington ammunition. These barrels are constructed from the finest domestically sourced steels, are drilled, reamed, and button rifled, and then profiled and chambered to exacting dimensions in compliance with SAAMI Specifications. This high-precision manufacturing processes ensure both accurate and repeatable performance for thousands of rounds.