Flatted primer are normal in 454, 460 and 500 S&W. primers.

Case will start to become sticky at just over 60kpsi.

You case extraction as a guide to load pressure on these cartridges.

The crimp won't make more the 1000 psi difference in peak pressure.

It will be easy to demonstrate.

Load a case and don't crimp- shoot make you primer observation and you will see it is no different than those you crimped.

Mr Stevens posts are on the money.

be safe
Ruggy