Mec 600jr. Die Set .410 Bore Pre-mark. To form a bottleneck the dies are heat treated and each have a molded cavity to hold one or two cases firmly in place. The dies have been carefully made of steel to ensure a lifetime of durability. To form a bottleneck the dies have been heat treated and the shell crimpers are oil crimp with a knurled mouth that allows the reloader to manually fine tune the necks until they near maximum concentricity. Because the necks of the cases near the shoulder are only slightly concave the dies have been enlarged a small amount of the case mouth remains uncrimped to prevent damage to reloading dies and cylinders. To allow the reloader to fine tune the necks must be resized. Specifications for Mec 600jr. Die Set .410 Bore Pre-mark V: Manufacturer: MEC Caliber: .410 Bore Fabric/Material: Steel Gun Type: Shotgun Package Contents: Mec 600jr. Die Set .410 Bore Pre-mark V The Mec 600jr. Die Set .410 Bore Pre-mark V is a quality addition to the MEC lineup. For more great deals on Reloading Dies by MEC please browse our Mec Reloading Equipment page.