I've been saving brass for years from a 7mm rem mag i inherited anticipating working up a load for it.. It's just occurred to me, years back I had to replace the barrel on it with a new factory rem barrel, but failed to separate my brass from the old barrel to the new one. I'm waiting on a set of headspace comparitors....will I be able to decipher through measuring the headspaces, necks and shoulder diameters, oal etc. Which brass are from the old barrel? I'm assuming there's no way the barrels are the same. I do have some brass that I know for sure are newly fired...I would be using those as my base line...I should be able to pull this off shouldn't I ??