Re-phrase: dummy round test.
Grab the base in a collet ?
I assume Adjust base as needed to get 0 run out, check further down body /neck/ bullet
what is good .001 ?
Thanks
A lathe would not really be the ideal tool.There have been many hand held, jig fictures made for this purpose. A lathe would be very slow, and you are dealing with an all brass, copper assembly. That is quite plastic as materials go.
I just ordered a concentricity gauge from 21st Century. Very clever design, it also uses a test indicator instead of the typical dial indicator. You can buy it without a test indicator if you already have some.