Donie, that's exactly what I wanted to know. If I wanted to crown a barrel, could I out the chamber in the spindle with a snug fitting collar and use the 4J to indicate the muzzle true?
Given the distance between the muzzle and chamber, I think even a loose sliding fit 20" away from the working end would provide very little angular runout.
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This is what I have done so far, first read up some on how gunsmiths deal with gun barrels, then found an approach that would work with the equipment at hand.
The problem,
If a 18" barrel is held in a four jaw chuck, so as the end protrudes 1" from the jaws for crowning or working the chamber end, the other end will be unsupported inside the spindle.
Also, the OD of the barrel may not be concentric with the bore.
So, I thought it would be more ideal to locate the bore using a pin in the end of the snug fitting plug I made, rather then using a bushing around the OD of the barrel to prevent the barrel whipping or bending inside the spindle. Here, keep in mind I am using an EE, When I can, I use high speeds for the finish along with accuracy.
Now, with the machined plug inside the spindle, equipped with a pin to tightly fit the barrels bore, I push the barrel and plug back into the spindle, then using a four jaw chuck with lead pads on the jaws, true the barrels bore using another pin.
A Note on the plug, I gave it less then .001" clearance to the spindle bore, then grooved it at each end for Orings, to help keep it from drifting within the spindle.
Also, I made the plug so I can change the pin size for muzzle and chamber ends.
I wanted to try out
an 11 degree crown, but thought I would end up re-cutting it to 90, more typical with a 22lr, it worked out, so I left it there.