If you are putting the calipers across the 5 groove rifling impressions you will be getting a larger diameter than it actually is. There is a way of doing it with V-blocks but for sizing for cast you need an accurate throat diameter.
I use the pounded or impact slug method described below, taken from the Cast Boolits archive.
Another alternative (prefered by 45 2.1) is a pounded slug. One fills a fired case with a hard lead alloy leaving just a little of the neck empty, and then drives a soft lead slug into the lead/case/throad area. Using a brass rod of near bore dimensions if the best driving road. There are other ways to get the same pounded slug, but this is the way that worked best for me. Lube the bore and outside of the case and use a heavy hammer to pound the slug into shape. there is no shrinkage doing it this way.
already put slug down the chamber into the rifle , its 2 band , then remove slug i measured the two bands that were stcking out ...and got the reading of ,318
Last edited by gtpkeeper; 31-08-2017 at 11:28 PM.
ballkeeper