The Sinclair Shoulder Bump Gage Insert #40A is a precision reloading tool designed for 40-degree shoulder cartridges specifically engineered for 25-338/Ackley cases.Sinclair Shoulder Bump Gage Insert Model #40A40-degree shoulder angle specificationDesigned for 25-338/Ackley cartridge casesPrecision machined for accurate shoulder measurementCompatible with Sinclair bump gage systemsEssential for handloaders working with Ackley Improved cartridges ensuring proper case shoulder positioning and consistent chambering for optimal accuracy and case life.