This may be a little to old school for some people, on this side of the pond old good quality files that are past there best is a good source of quality steel for manufacturing gun parts. I cut the required length of the file with an angle grinder then heat to cherry red then allow to cool slowly to bring it to soft condition. I have found this type of steel will oil or water harden. In a short film about Holland and Holland works the stocker did mention that he made his chequering tools from old files, good to see the practice of making things from old files is still alive and well here.
