Introducing Shilen's custom Large Format AR (LFAR) barrels with Drop-In convenience. Each LFAR barrel is machined using the same processes that have helped Shilen customers win endless competitions and set so many World Records over the years. Each barrel is assigned a bolt assembly and then chambered to the correct headspace for that bolt. Gas-block shanks are machined to +- .001 for proper fit. Each barrel is uniquely numbered to match with its' corresponding numbered bolt, and the barrel extension is installed. Shilen has improved the functionality and durability of their Drop-in LFAR's by moving to a high pressure bolt (9310 hardened steel) with included matching firing pin.