If you are building a gun to look like new, rather than brown the tips of the screws at the lockplate, heat blue them...also known as nitre blue if you do it in a bath of nitre blue salts. I have a US Mississippi Rifle dated 1853 on the lockplate, and the screws were all heat blued, and still show it inside the inletting. If you cast your own balls, the melting point of pure lead is about 620 F, which is just over the color change point on steel to a peacock blue. Put the screws a couple at a time into a shallow steel or stainless steel container, like a tablespoon with a bent-up handle, and place the container bottom slightly into the surface of the lead. Watch for the color change and remove when it's where you want it.
David