- The HMB Bolt by HM Defense eliminates the pass through cam pin hole and replaces it with a cam pin socket and radiused cam pin design. The new patented design eliminates the natural weak point of Mil-Spec bolts by significantly increasing the amount of metal (and strength) at the cam pin location. The result- NO MORE BROKEN BOLTS! The HMB Bolt also reduces contact between cam pin and firing pin, enabling smoother operation of firing pin, bolt lugs and aft gas rings. The new cam pin socket also retains lubrication for extended operations.