The Sinclair Shoulder Bump Gauge Insert #40 is a precision reloading component designed specifically for 40 Degree Ackley 6mm cartridges to ensure accurate case preparation.Sinclair Shoulder Bump Gauge Insert #40Designed for 40 Degree Ackley 6mm cartridgesPrecision machined for accurate shoulder measurementEssential tool for proper case headspace adjustmentProfessional-grade reloading componentThis specialized insert enables reloaders to precisely measure and control shoulder bump for consistent cartridge dimensions and optimal chamber fit in 40 Degree Ackley 6mm rifles.