Hi, I haven't done my sten mkII build yet, but I was going to follow the SGN build from a few years ago with a few changes. He annealed the bolt for that build. I have modified suomi bolts to semi. Other sites have listed the suomi bolts at 55RC and to machine them I also annealed the bolt. I haven't heat treated the bolts yet and don't know if I will as I seriously doubt I'll put a ton of rounds through them. If I did re heat treat them I wouldn't try to make them as hard as they were initially just in case I accidently made them too hard and they would crack.