Case Head Separation

A case head separation is a brass failure in which the case parts circumferentially in the web region, just ahead of the solid case head. It happens when that area thins from repeated stretching, which occurs when the case is pushed forward in the chamber on firing and then sized back too far each cycle. A bright ring around the outside of the case, or a scratch you can feel inside with a bent wire, warns that the web is thinning before the case fully fails.

The usual cause is excessive headspace clearance combined with aggressive full-length sizing that sets the shoulder back too far each time. Controlling shoulder bump so the case is pushed back only slightly keeps the web from working itself thin and protects against this failure. A full separation can vent hot gas back through the action, so inspecting brass for the telltale ring and retiring suspect cases is a basic safety habit.