I had a .270 Ruger that had such generous chamber dimensions that neck sized brass would not fit in the other 270s. I don't think going to an AI would have cleaned it up with out setting the barrel back several threads. Most expansion was in the base area. If yours is like that you are working the web area each time you FL size it. Brass can age harden especially if subject to any heat. Also any fumes can weaken the brass. I left some muriatic acid open and cartridges stored on the shelf below had to be chucked.

Just for grins I would check both chambers or compare fired brass to see how far off they are if any.

"When you disarm the people, you commence to offend them and show that you distrust them either through cowardice or lack of confidence, and both of these opinions generate hatred." Niccolo Machiavelli