GUNSMITHING SERVICES: 8-40 Optic Base Threads for Remington M700 and Winchester M70
A nagging side effect of production grade receivers is the tendency for certain features to be machined slightly out of position. The 8-40 optic base hole upgrade is intended to resolve this issue.
By aligning the receiver bore to an axis on the milling center, we are able to correct position errors on the receiver. Then we go a step farther. The traditional process is to chase the existing holes with a drill and complete the job by tapping to the 8-40 thread pitch size.
LRI has altered this process. Here we bore the existing holes to size using an endmill. Doing so ensures that the hole is truly on position and not merely made larger by a drill. Drills are good for establishing the size of a hole. Boring ensures ensures both location and size. We complete this process by milling the threads. Thread milling is similar to boring the hole, only now the thread size and pitch is created with a single point style tool.
The end result is optic bases that are parallel to the receiver bore. This reduces windage errors, allows optics to remain closer to their mechanical center point, and ensures that optic bases attach to the action in the correct manner.
This service is offered in two ways. One is a stand alone where this is all we do. The 2nd is as a compliment to our accurizing service. The setup work is where the majority of the cost originates from. We follow the same procedure that we use to accurize an action as it is the only way to ensure we get it right.
The two different price schedules reflect the setup work involved.
This video shows segments of the thread milling operation:
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