In reviewing loads for the 500, I see that people always list the LR primer that they used ...are there rules for interchangeability in primers? I know some are hotter than others and what not, but I'm a newbie at this. For example, there's one load that I saw with CCI LRM primers, but I own Fed 210M primers ...any problem in using the Feds? What's the story on primers and how they differ, i.e. in terms of chamber pressure and velocity?