Advice on a reamer neck diameter

[40X Guy]

Ready to get a reamer ordered for my new build, and will be using Norma brass in my .220 Swift. Loaded new brass is miking at .253, what would be the smallest neck diameter reamer to order based on this spec? I don't want to turn necks, but I don't want headaches with too tight a neck diameter, this rifle to be a dedicated long range Varminter, and very casual paper puncher. Looking at either .256 or .257, which way to go and why? Thanks!

Frank

 

[RonAKA]

I would load at least 20 rounds and measure them all twice at 90 degrees to the first measure to the 1/10th of a thou, and add 0.003 to the largest dimension you get. If you end up in no man's land split between even thou, then round up rather than down.

 

[fdshuster]

Frank: As Ron said, measure a number of loaded rounds, and with all brass you will be using, and to the largest diameter I personally would be comfortable with .003" larger. Small enough to be beneficial to extending the case life, better fit in the chamber, etc., but not so small as to cause problems even if you run into the very rare case that may have neck walls just a tiny bit thicker than "normal". I've been using that .003" dimension on all my tight, no-turn neck chambers for years and never had a problem. If you are spec'ing a new reamer be sure to also specify the chamber over-all-length otherwise you could get a chamber length that is .030" to as much as .040" longer than maximum case length. I specify .010" longer than max case length: 6BR case at 1.560"/ chamber length of 1.570", for example. To me the freebore dimension is very important and I load a dummy round with my first bullet of choice, seated with the base of the bullet at the neck/shoulder junction, and specify that the bullet be touching the lands.