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Action Truing

Shown below are methods used to set up an action in the lathe to single point true the threads, receiver face, receiver lugs, bolt face and bolt lugs. There are other methods that can be used to true an action using some pretty expensive tooling from either Manson or Pacific Tool & Gauge that use piloted reamers and piloted taps. As long as the pilot used fits the receiver well front and rear, I have been unable to tell that an action trued using one method or the other shoots any better than one trued with the other method. Lets face when an action is true, it's true. When it's not it's not. How you get to that point doesn't make that much difference. It's the results that matter. When a barrel is installed on an action that is true, the barrel will shoulder up and then it very little rotation of the barrel from just touching the shoulder until it's fully tight. When action isn't true, the barrel will hit the shoulder and then turn quite aways rotationally before the barrel is fully tight. In this case the shoulder is forcing the threads out of line with the receiver face to get the barrel to shoulder up tight. Any time a barrel is fired, there is lots of pressure put on the threads of the barrel making it move in the receiver. If it doesn't come back to the same place every time, the barrel won't shoot. The receiver threads being square to the receiver face is probably one of the most important things that has to do with rifle accuracy. How square the bolt lugs are and the bolt face are to the receiver centerline may not have quite as much effect on accuracy as the receiver threads being true and square, but how true they are to the receiver definitely has an effect on how well the and smoothly the bolt opens and closes after the cartridge has been fired. A bolt that locks out of square is working against the fired case to open resulting in hard bolt lift. A bolt face that is out of square does the same thing. The hotter the loads the more apparent this becomes as the brass doesn't spring back as much as with lighter loads. On a short range benchrest rifle, the bolt face being out of square as much as .001" can make a difference as to whether the bolt will work freely or not when shooting some of the hot loads that are currently popular. I have recently added the Pacific Tool and Gauge the oversize piloted tap to fit the Howa and Weatherby Vanguard actions to aid in truing these metric threaded actions.

collet Indicating the receiver bore for minimum run-out
This shows the collet that is placed around the receiver
to keep from marring the finish of the receiver.
Indicating the receiver bore for minimum run-out. A
tight fitting mandrel is a necessity.
indicating collar receiver locking lugs
Facing the front of the receiver. The receiver
is held in the indicating collar.
Set-up to face the receiver locking lugs.
receiver threads Drilling
Single point re-cutting the receiver threads.
Drilling receiver to pin Holland recoil lug.
bolt body Truing the bolt locking lugs
Indicating in bolt body. The bolt is held with
threaded ball similar to a construction ball.
Truing the bolt locking lugs.
dial indicator Truing bolt face
Adjusting steady rest to true bolt face. The dial indicator is to
check that the bolt body doesn't move when steady rest points are adjusted.
Truing bolt face.
The end result of precision machining Indicating collars
The end result of precision machining. Full contact of both locking lugs without lapping on this receiver. If lapping, is required after truing, it will take a very minimal lapping to make full contact with both lugs. Indicating collars used for truing other actions. About the only action I won't true is the Ruger 77 Mk II.
End view of indicating collar Stiller Diamondback
End view of indicating collar shown above.

New in 2012, I purchased the Trubore alignment chuck and started using it to true my receivers. It still uses the tight fitting mandrel with two dial indicators and adjusts similarly to the original fixture with eight set screws to get the receiver raceway aligned for truing the receiver. It's probably not for the hobbiest as it's not a cheap setup, but does excellent work. It does seem to be a little more time consuming to adjust than the set screw method. I do like that the six jaw chuck, holds the receiver very securely and makes sure that nothing moves during the truing operation. Click on the photo for a larger image.

Bryant Custom Precision Riflesmithing  
Bryant Custom Precision Riflesmithing