Product Description The Proof Research 128657 AR-Style Barrel in 6mm ARC represents the pinnacle of precision barrel manufacturing. Built on a full-profile, match-grade 416R stainless steel blank produced in Proof&';s own firearms division, this 16" rifle-length barrel is turned down to a significantly reduced contour and then wrapped in high-strength, aerospace-grade carbon fiber impregnated with a proprietary matrix resin developed by PROOF Research ACD. The result is a composite barrel that is stronger, lighter, and as accurate as the finest precision steel barrel available. Carbon fiber&';s unique ability to diffuse and transport heat through the barrel wall greatly enhances heat management, extending barrel life even under sustained fire. With a 5/8-24 muzzle thread, .750" gas journal diameter, and optimized for use with a Grendel Type II bolt, this barrel is an exceptional choice for any serious AR-platform build or upgrade. Product Highlights Full-profile, match-grade 416R stainless steel core wrapped in aerospace-grade carbon fiber for outstanding accuracy and durability Up to 64% weight reduction compared to standard steel barrels, coming in at just 1 lb 12 oz Proprietary PROOF Research ACD matrix resin provides superior composite strength and resilience in demanding environments Rifle-length gas system with .750" gas journal and 5/8-24 muzzle threading for seamless AR-platform compatibility 1:7.5 twist rate optimized for 6mm ARC with Grendel Type II bolt compatibility for reliable cycling Specs Brand: PROOF Research Caliber: 6mm ARC (6 ARC) Barrel Length: 16" Twist Rate: 1:7.5 Gas Length: Rifle Gas Journal Diameter: .750" Port Size: .096" Muzzle Thread: 5/8-24 Finish: Black Carbon Fiber Material: 416R Stainless Steel with Aerospace-Grade Carbon Fiber Wrap Weight: 1 lb 12 oz Platform: AR-Style Bolt Compatibility: Grendel Type II UPC: 843068128657 MPN: 128657 Disclaimer: We strive to provide accurate and up-to-date product descriptions, specifications, and images; however, errors or omissions may occasionally occur. We are not responsible for any inaccuracies or discrepancies in the content provided. If you notice anything incorrect or unclear, please contact us so we can correct it. When in doubt, we recommend verifying details directly with the product&';s manufacturer.