I'm kinda new to machine tool (two semesters) and haven't got into the types of steels and what their properties are yet (I need a book on this). What type of steel would be best to make a hammer or firing pin of? I need something that won't deform or break and can take several blows in fast succession like a semi-auto could do. What would hold up to repeated pounding and not break or deform, A2, D2 or some sort of spring steel? This part will be small and the way it is made extra material for reinforcement can't be left on it and weight is not an issue. Any suggestions?