Also referred to as blue printing, truing an action is a process in which a less than perfect factory actions surfaces and contact points are machined to tighter tolerances, proper geometry and perfect alignment.
For the purposes of this article we’ll use the factory Remington 700 action as our example. A Remington action may perform very well out of the box. However, most often the thread geometry inside the receiver where the barrel meets the action is less than perfect. The threads can be cut poorly or are sometimes not concentric to the bore axis. Part of the truing process involves opening up these threads by re-cutting them to a proper and perfect thread that is concentric to the bolt way.
We start by dialing in the action on the lathe.
Then we cut the threads inside the receiver.
The face of the action and recoil lug can also be less than perfectly perpendicular to the bore axis. This can cause the barrel to be misaligned with the action. To correct these issues the material on the front of the receiver is squared to the bore axis. The recoil lug can either be ground perfectly true or replaced with an aftermarket lug. Often people will opt to replace a factory recoil lug for an aftermarket thicker lug especially for heavier recoiling calibers.
Like the front of the action, the bolt face is also trued so that it is perfectly perpendicular to the bore axis. This ensures that contact between the cartridge and the bolt face is uniformed and even. This process can even be performed on bolt faces with riveted extractors as seen here. The bolt lugs are cut perpendicular as sometimes the lug sides are crooked and hit the receiver. Finally, the bolt lugs are lapped to verify and improve surface contact. This results in a smoother action and better performance.
Once the action is trued we can begin the barrel installation.