Hi Joe like JDW said I also use drill rod though this side of the water it is called silver steel. I harden the steel in the usual way after turning heat to cherry red then quench it in light oil rather than water doing it this way I find any metal warping is kept to a minimum. Then I draw the temper to deep blue and quench again, this leaves the strikers harder than the un-treated steel and imparts some natural spring to help it cope with impacts. Though some replacement firing pins I have made are extremely thin and also have a waist then I turn them well over size heat treat them which nearly always ends with them warping then bring them to final size using a small tool post grinder. I have used carbide tipped tools to bring then to the final size after hardening but that really depends on the pins size because if they are too small the tool pressure can cause the pin to break. I feel I must add here that grinding in the lathe is a large NO NO unless you take real care not to get grinding grit in the lathe ways and slides.
