Check the drawings for both cartridges.  As far as I know, the gages are the same.

The gage makers publish a cross reference on their sites, too.

from PT&G:

6mm Creedmoor, 7mm Creedmoor, 30 Creedmoor, 338
Creedmoor use the same gage as 6.5 Creedmoor

Go here for a copy of the cross reference:

http://pacifictoolandgauge.com/content/11-file-downloads

Where are you getting the fired case?  Where did you set the headspace of the formed case?  What is the difference in the headspace of the formed case and the fired case?  Were these fired in a barrel chambered with the same reamer as the new barrel?

Headspacing on cases is not a great practice, and I know it is common enough.  Gages are not expensive compared to everything else required to rebarrel an action.  A barrel installed to minimum headspace is not a pressure liability with factory ammunition.  One with a tight neck is a problem when considering factory ammunition.  Headspacing on brass is a good way to arrive at a chamber that is shorter than minimum headspace, even if the shoulder is not set back while closing the bolt, the shoulders and body are springy.