I am taking my barrel to the local gunsmith to be rechambered from 308 to 300 win mag. heas asking me to purchase a set of headspace gauges but saysI dont have to bring the receiver. Im Kinda confused. Ive rebarreled three dozen of my own Savages and understand the head spacing. My question is when he rechamberes it does the Belted part of the brass go inside the chamber or does it ride/rest on the outside on the barrel....Thanks for any help