Neck Turning Dims? Thoughts?
 

Generally I have only neck-turned for rifles that I either had the reamer or a chamber casting for, but I'm considering turning some crappy rem brass for my wife's Savage 12 and getting a bushing die set up for it.

Not wanting to go through the expense/hassle of casting the chamber, I was thinking out loud about ways to mic or measure the chamber throat, when my wife, of all people, asked "why can't you just use my fired brass?"

I can't argue with the logic. I'm sure the case mouth springs back a bit so I may start a little larger dimension, but I'm thinking if I measure an average of her fired brass, then add bullet diameter, subtract out a little crimp tension, that should give me a pretty good idea of where I should be fore neck thickness?

Am I missing something? Thoughts? Suggestions?

Only two instances that I ever have to turn necks. I have a custom cut chamber on a 6mm 30-30 AI Contender barrel that requires formed brass to be turned and I turn necks on .223 brass that I make .221 FB out of.

A good tubing micrometer is handy for reference and to check concentricity.

In the case of the 6mm I have a known chamber neck dimension. I get about .002 " neck tension with sized brass and a loaded round gets a release of .0015" to .002" clearance when fired.

In the .221 I used the "trial and error" method to get the round to chamber and get the release I was looking for.....neck tension is whatever it is.