CJ, if you're referring to the Lyman "M" die, it does not decap or neck size your brass. You must use a standard FL die leaving the neck expanding button out of the process. Then run the case into the "M" die to expand and make the step in the neck. Some dies cannot be used without an expander button, there would be nothing to hold the decapper pin. Then you must use a universal decapper die, then use a FL die with the decapper rod removed.
Maybe you already knew this, but the way you wrote that, I didn't want a new reloader to get confused