This may or may not apply, but when switching from lighter commercial cases to heavier military cases in .308 or .30-06.......the NRA reduction formula calls for taking 12% of the case weight difference and reducing the powder charge by that amount.
So in your cases, the PMCs should be reduced by .6gr of powder. This may be overkill, but it does give a safe, reliable starting point to figure out what you need to do.