have lots of brass that has been loaded many times,,, myself every 3rd loading i anneal the mouth of my cases,, handgun and rifle ,,, with handgun just the first 1/8 inch of the mouth,, with rifle the whole neck ,, depending on how much you work the neck or mouth of the case in resizeing makes a big diff in life of the cases,,,check a fired case dimension against the size of a fully sized case,,,(check the manuals or with manf) if to much diff you work the brass too much and reduce case life,,,(myself, because of more then one gun for the same calib. and more size diff then i prefer) i prefer to send a fired case to RCBS or whom ever u get yours from and have them make a sizeing die for that gun,(i mark my boxes of bullets for a particular gun) (maybe a bit anal but it works), a couple dollars more, but more life of brass and better accuracy.. remember they make the dies so that all bullets will fit all guns,, depending on how old it is and manf tolerences, can have large diff in chamber sizes...hope this helps,, have fun