Blueprinting

Blueprinting is the gunsmithing process of taking a factory action and re-machining its critical surfaces back to a true geometric ideal. The receiver face is cut square to the bore axis, the threads are single-point cut concentric, the bolt face is trued, and the lug seats are lapped so everything that locks together sits perfectly perpendicular and aligned. Mass-produced actions leave the factory with small tolerances stacked in random directions, and blueprinting removes that slop.

The payoff is a foundation where the barrel threads on dead concentric and the cartridge sits square to the bore, which removes a source of inconsistency before the first shot. It is a core step when a smith sets out to accurize a rifle, closely related to barrel truing, and it usually goes hand in hand with a properly fitted recoil lug.