The most common problem with reloading belted magnums is when people adjust their resizing die down against the shell holder. This pushes the shoulder back and headspaces on the belt. This will split cases and shorten case life for sure. I have talked to many shooters that thought doing this would make their cartridge smaller so that they would chamber better. (They've found out that it doesn't work). Try this test using just "one" case: Reload a new case, fire it, reload it, and measure the area "just above" the belt. Then repeat the process again and again until the case won't chamber. You will find that every time that you measure the case, it has increased in diameter, in the web area, until it won't chamber. The reason that a conventional resizing die can't properly resize belted cases is this: In order to resize any given area on any case, you must press the die "slightly" below that area. Because when the case is withdrawn, it "springs back" a little bit. As long as a conventional resizing die has to stop at the belt .... it will never be able to fully reduce the case diameter "just above" the belt. Take a look at my web site www.larrywillis.com
where you can see the article that I wrote for Precision Shooting on this subject. I've spent a year researching this problem and designing a resizing die that would solve this problem with reloading belted magnums. My next step is to post a long list of product endorsements that I've been collecting to my web site.