All authentic iron or steel parts were forged, and not investment cast. No one cast steel by any means in the muzzle-loading era ("steel mounted" London Colts used cast malleable iron trigger guards).
Get yourself some reproduction parts, a Siler lock from Chambers would be a good place to start. All the internals are investment cast and the screws are neater than originals. Maybe a couple odd pieces of brass hardware, such as thimbles, sideplate, forend cap. Original wood screws were iron, never (never say never?) brass.
Original nipples had four flats, not two as on modern.
Many repro rifles have too much wood around the lock, and around the barrel breech as seen from the top.
If you are into percussion accoutrements get an Italian powder flask. Different screws holding the head to body, cast head vs formed & lsoldered head on antique, gate spring has square edges on repro, beveled on original.