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Torque Shoulder Lap

THE IDEA FOR THIS TOOL IS NOT MY OWN. IT WAS BROUGHT TO MY ATTENTION IN SOME PRIVATE E-MAILS WITH A COUPLE OF FELLOW FIREARM ENTHUSIASTS. WITH PREMISSION I MAY INCLUDE THEIR NAMES AND PHOTOS!

The Large Ring Mauser is one of very few actions to have TWO torque shoulders. When tightening a barrel into most actions, a single shoulder on the barrel tightens against a single shoulder in the action. Usually, the barrel is shouldered ahead of the threads and this shoulder tightens against the front of the action. This "joint" is visible, it's where the action ends and the barrel begins, at least externally. The LRM has TWO shoulders, one is the front of the action, and one is just ahead of the bolt face. The one on the front of the action is clearly visible (except in the case of the Turk 38 rebuilds or K.KALE actions where it is hidden by the hand guard retaining extension), while the internal shoulder is rather invisible unless the barrel is removed.

When barreling a LRM, the barrel shoulder should solidly contact the front of the action and the end of the barrel should solidly contact the inner shoulder. Also, these two shoulders should be parallel to each other and at right angles to the action threads. The shoulder at the front of the action is easily cleaned up and squared with the threads by using an action mandrel as shown HERE.

Squaring inner shoulder is not so easy, unless you have a tool like the one I am going to show here.

First, a body is made. I used brass, just because I had some. The end is threaded to match the action, the same as a barrel would be. The threads are cut to allow easy screwing-in by hand. The length of the threaded "shank" is 1/8-inch shorter than a barrel would be, so that when the shoulder contacts the front of the action, there is a 1/8-inch (0.125") clearance between the end of the body and the inner torque shoulder. I then bored a 1/2-inch hole through the body. All of this was done without removing the body from the lathe, to insure that the threads, the shoulder and the bored hole are true and square.

A piece of brass 0.100 inches thick is parted from a piece of stock.

The parted disk was centerdrilled and fitted to the end of a 1/2-inch piece of drill rod that had beed drilled, tapped and slightly shouldered. The drill rod and disk are mounted in the lathe and the disk is turned to a diameter that will just clear the action threads,

This is the completed tool, a "lap" if you will. The front of the disk, opposite the body of the tool, will be charged with 125-400 grit abrasive, the tool screwed into an action, and the drill rod rotated. This will lap the inner torque shoulder and insure that it is true with the threads and receiver face. 

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