13.7" is a terrible barrel length
The 13.7-inch barrel length for AR-15s is critically examined, arguing that while it meets NFA requirements with a pinned muzzle device, the need for longer devices negates the compactness advantage. Shorter barrels also present tuning challenges due to reduced dwell time. While 14.5-inch barrels are currently superior for reliability and flexibility, future designs might optimize the 13.7-inch configuration.









