From what i read- The web area is where the problem may be. When the chamber is a tight fit, it can cause hard bold lift. Some have the chamber in the area of the web opened a few thousandth, or buy a special die that sizes the brass/web smaller. The die has to size all the way to the extractor groove. The brass is much thicker in the web, as i am sure you know, so may take a strong press. The web should not expand much if at all. High pressure will do it. Showing up as loose primer pockets over time, may take more than a few firings. Some measure the amount of pressure/diameter increase on the web. If over .001" high pressure. Some say no more than .0001" is acceptable. What BoydAllen said about the WEB. 
