I had been mixing my 6.5 Creedmoor Hornady brass, and no worrying about Lot #.... It seems that there is a pretty good variation between neck thickness and size in different lot numbers. It has made sizing a pain. I try to size the shoulder 1-3 thousands from fired to prep. I have decided to buy several hundred in the same lot # and keep them together all the time when prepping and loading so as to get more consistency when sizing.. I assume all you top shooters do the same? Pipe in, please...