Ill-fitting, improper screwdrivers and the people who carelessly wield them account for the single most common job in the shop, making new screws. Few things can spoil the appearance and value of an otherwise nice gun the way butchered screw slots can. The procedure is as follows, turn the new screw from barstock on the lathe, leaving the head extra long. Then cut a temporary slot, install the screw with the proper torque and mark the height of the head and the final slot orientation. The excess head is cut off and then the screw slot is cut in a fixture designed for the purpose. The screw is reinstalled and the head is carfeully contoured, then the screw is removed, the appropriate engraving is performed and then it is appropriately finished and if needed, the finish is artificially aged to match its surroundings. I use a 20X microscope and push gravers to do all of the engraving.
Here are some examples from an Ithaca Baker model SBT.
These are the triggerplate and breech screw s for a Crown grade L.C.Smith.