HM Defense has announced that their new HMB AR-15 bolt is now available for purchase. What makes it different is that instead of having a cam pin hole it has a cam pin socket. In other words, the cam pin hole in this bolts is not machined all the way which increases the amount of material in one of the weakest portions of the AR-15 bolt.
Even if you haven’t encountered such a failure yourself, just type “AR-15 broken bolt” in your search engine and you’ll probably see many results with bolts broken in half right in the middle of the cam pin hole. Just like this one:
The HM Defense bolt is designed to reduce the probability or completely eliminate this issue. Because the cam pin hole is not completely machined it has additional supporting material in the bottom. It also has a proprietary tapered cam pin. Other features advertised by the manufacturer are the ability to hold the lubricant in the socket for a longer period of time and the reduced contact of the cam pin with the firing pin which is supposed to decrease the friction between the parts and ensure smoother operation.
Here is a video review of the HMB bolt.
The HM Defense HMB bolt comes with its own cam pin. It is a drop in part compatible with MIl-spec bolt carriers. The bolt is made of 9310 steel and the cam pin is made of 4340 hardened steel. Both parts are nitrided. The 5.56NATO/.223Rem version of the bolt is available for purchase at an MSRP of $85. Right now you can get it at a special introductory price of $69.