Thanks Muznut 54, and Quickdtoo,
I have now measured in both ways you have described, and they concur at .015. I also have very tight frame to barrel fit.
Thanks, Tim, for the .006 on the maximum slop, as that was one of my questions.
Muznut, I am glad to hear from you, as you are the man who alerted me to the problem.
I still have one question remaining; and that is how many of these left the factory this way? I suspect that it may have been the lion's share. So I would still like to hear from any others who have 500s. .015'' is big, and you can see it's excess, even before you measure.
On this barrel It also had the rear sight (which I will be using) mounted far right of center. Very sloppy and disappointing workmanship. It's a factory; make a mounting jig, so that all holes will be drilled correctly. Don't guess at it.
I should not have to drill and tap new holes and remount the sight. But I did, and it was no small feat, as I am neither a machinist, nor the son of a machinist.
Now I will have to fill this excess headspace with JB weld. Yes, it's lame, and will be a pain in the ass, but I still prefer that to sending the barrel back.