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What concerned me is that the instructions that came with the RCBS dies say that too heavy of a crimp can damage the case.

I have a question about the Lee Crimping Dies. I looked them up in Cabela's and the description says ""the carbide sizer sizes the cartridge while it's being crimped". I don't understand why I would want the cartridge to be sized after I have already sized it, expanded it, and seated the bullet.

Would I use that for a separate step after seating the bullet? Will a Lee die fit in a RCBS press?

That is bogus information about the Lee Factory Crimp Die on the Cabelas website. Look at these descriptions and there is nothing about sizing:
http://www.leeprecision.com/html/catalog/dies-crimp.html
http://www.leeprecision.com/cgi/faq/index.cgi Go to Dies and die questions, then Factory crimp die adjustments and Factory crimp die advantages.

You learn something new everyday whether you want to or not.