What do you do to true an action?
I use a method that is similar to the method that Greg Tannel has developed and markets commercially. I do use his piloted reamer, but mostly I use it as a mandrel for indicating the receiver in the lathe. In practice, it’s used with two tight fitting bushings that fit into each end of the bolt raceway in the receiver. I then use two dial indicators with a special indicating fixture that I developed to “dial in” the receiver true to the lathe axis.
At this point, all truing cuts are done to the receiver. The receiver is faced with a truing cut across the front of the receiver ring. The receiver lugs are faced with a truing cut across the lugs and then the receiver threads are re-cut with a single point threading tool. All truing cuts to the receiver are made on one setup and are made true to the receiver centerline.
The bolt also needs to be trued and I use two dial indicators to ensure that the bolt is running true to the lathe axis before truing cuts are made on the bolt lugs and bolt face.
The last steps to truing are to either surface grind the original recoil lug or substitute an aftermarket trued recoil lug. Regardless, of which lug is used, I check the lug with measuring instruments for flatness.