Squaring Torque Shoulders

[Clemson]

In working on the current M48 action in preparation for rebarreling, I ran into a situation that I did not anticipate. Naturally it slowed me down at a very bad time. I have a "Go" gauge on loan from Flaco because I can't locate the one that I know I have, and Flaco has a barrel on the way that he needs his gauge for. I promised to get it right back to him, but I ran into this........

 

The first step is to square the secondary torque shoulder. That is the one on the front of the receiver ring. It is machined by installing the action on a mandrel so that the machine work is perpendicular to the threads. This shot shows the action on a Brownell's large ring mandrel swung between centers:

 

The idea is to cut a square area that you can use to take measurements from. You don't need to cut a bunch from the front ring.

 

Measurements are taken with a depth micrometer. You would like to have the distance from the secondary shoulder (that you just dressed off) to the primary torque shoulder (aka the "C" ring) to be equal all the way around.

 

Unfortunately, this action, a Yugo M48, is off by 0.0035 inches from side to side. That is unacceptable. Page 163 in Kuhnhausen's Mauser book shows a tool that he made up for squaring the shoulder. I decided to make one similar. The first step was to sacrifice a 98/22 barrel that I had in the corner. This shows the collet set-up for holding the muzzle end of the barrel:

 

The next step involves setting up the steady rest on the breech end of the barrel"

 

I ran a 31/32 drill into the chamber end about 3":

 

I followed the drill with a 1/2" reamer:

 

I parted off the breech end to make the body of the tool:

[Clemson]

The next step involved making a shaft for the tool. I used a piece of 1/2" hot rolled steel rod. I drilled and tapped the end of the rod for a #10x32 screw. Next I cut a disk from a piece of 1" ground and polished stock to make a washer for the end of the shaft. The completed shaft and tool body look like this:

 

Assembled, the tool is shown next to a jar of lapping compound that I am using to lap the shoulder:

 

I installed the action on a HoleShot receiver jig and held it in the vise for hand grinding. That was way too slow for the amount of metal removal that I had to do.

 

I ended up setting the same rig up so that the drill press turned the lapping tool. About 3 minutes of that cut the shoulder down to a tolerable difference. You get about 0.002" of crush when you install the barrel. I got the primary shoulder parallel to within less than this amount and stopped there. We shall see when we shoot the final product if I took enough off.

 

Clemson

 

[sonic1]

tools ....tools....tools... it must be nice to have tools...nice job thanks for posting it

[Clemson]

Ha! After nearly 40 years of building guns, I finally bought a lathe. The drill press cost me $75 at a pawn shop. A bunch of my tools are homemade -- as evidenced by the lapping tool.

 

Clemson

[donmarkey]

That's the best kind of tools to have "homemade". You learn more by making tools than using them. Great job and pics, BTW I'd love to find a diamond cutter like he uses in his book.

-Don

[carzngunz]

Clemson,

I worked on a couple of K-Kales that looked like the barrels had never touched the inner shoulder. They were rough and scary looking. I made up a tool similar to yours, but as rough as they were, I ended up using some fine grit, adhesive backed, closed coat sanding disks on the end. If you take your time and don't apply too much pressure you can get a good and accurate job. Both of mine ended up at less than 0.001" difference. I was very pleased considering the original condition.

[flaco]

Clemson-

 

I was glad to be able to help.

 

And... really nice tutorial.

 

flaco