The Continuing Adventures of a Home Shop Machinist  
      After a little cleanup it's time for the calibration.  You'll need the jig and collar, an unmodified breech plug and 209 primer, and a depth micrometer.  Make sure that the plug/primer combo actually fits your rifle, since this will be the calibration standard that you'll use.


      Mount the plug in the jig, and tighten it securely.  Then  insert the primer, and mount the new collar on the jig.  With the depth mike, measure down from the top of the collar to the top of the primer.  The distance you measure here is the distance that you should get with a .25 ACP cartridge in a modified plug.  If you have several plugs/primers, check them all in your rifle and then measure the best-fitting ones - or just measure six or eight combinations and take the average.

      Once you've got this dimension, stamp/scribe it on the side of the collar; and if you think you might ever make another jig, mark this pair so you can remember which pieces go together!