This is a problem with once fired brass that was not fired in my own rifle. A mix of random rifles at the range, not just one troublesome rifle. Cases are once fired, mostly Federal .308, as well as some other brands, including once fired Lapua. After resizing, I noticed that some cases don't want to go into my Giraud shell holder for trimming. Upon close inspection, I see these cases have formed a burr-like lip on the outside of the case mouth, which prevents them from entering the Giraud case holder all the way. The cases with the lips measure 0.341 at the outside case mouth, while the trimmed cases that already entered the Giraud case holder and got trimmed, come out with the outside case mouth measurement of 0.335 This excessive lip is observed only on once fired brass that I picked up and full length resized in the RCBS small base die which is equipped with a Lyman carbide expander ball. Sometimes I get about 50 per cent rate with the lip, sometimes zero per cent. Once I use the cases in my own rifle, and resize them again, this lip is never formed again, or at least is not formed to the extent that i can't insert the case into the Giraud case holder. From what I can tell, the only way to remove this lip is to use the Lyman deburring tool to shave it off. I'm wondering if this lip is formed in my resizing die, in other people's rifle chambers, or is it just what once fired brass is supposed to be like due to some effect of factory ammo manufacturing. My goal is to avoid the lip so that I can easily and conveniently use my Giraud case trimmer on once fired brass that I can pick up at my gun club.