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Concentric Threading

July 24, 2017

Another critically important accurizing detail is insuring that the barrel threads are parallel to the bore and chamber and equidistant in their entire circumference from dead center of the bolt bore (i.e. concentric).


If the barrel threads are not exactly parallel to the bore and chamber, the bore and chamber will not be held square to the bolt face. This can only be accomplished by first trueing the action with a mandrel and action sleeve and then single-point cutting the receiver and barrel tenon threads. Chasing receiver threads with a "tap" is not precise metal work and does not meet with my standard for accuracy riflesmithing.


The threading of the barrel tenon is done after the chamber is reamed. Set up between centers, this then sets the center line of the bore and chamber . When the threads are then machined, they are concentric to the chamber. As a result, the chamber is held centered to the bolt bore race way.
When the barrel is tightened to the receiver, the chamber and bore is directed and held straight away from the bolt face.
 

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