Omid,
There is a potential for having over pressure loads when working up loads with 1x brass, then loading the same load in new brass, particularly when changing brands of brass. New lots of brass by the same manufacturer can vary in thickness and brass by different manufacturers may vary a lot in thickness. Hot loads worked up w/ 1x fired brass may result in a dangerous pressure load when using new brass from a different manufacturer.
I generally buy a lot of brass, work up loads with it new, use until time to discard brass and then repeat w/ a new lot. Established loads can easily be checked with a quick powder spread work-up and a chronograph to ensure they are safe with the new brass. In my opinion it's worth checking to ensure you won't have a problem.
HTH
David
