Looking at a used MasterpieceArms chassis which includes both a 6.5 Saum and Creedmor action.  At the risk of sounding like an ignorant fool I have questions.

Looking at a PDF from MPA it appears that changing from one action to another is a simple process.  I make the following assumptions:

1) since both SAUM and CM are 6.5, barrel change is not necessary
2) action change is necessary to accommodate the slight difference in cartridge dimension (i.e. headspace)
3) I've seen no mention of mag change, so that is also unnecessary

Are these statements correct?

1) since both SAUM and CM are 6.5, barrel change is not necessary - not true, the chamber is part of the barrel
2) action change is necessary to accommodate the slight difference in cartridge dimension (i.e. headspace) - not true, both run in a short action
3) I've seen no mention of mag change, so that is also unnecessary - ?? The MPA takes AICS pattern mags

I’m confused. Are these barreled actions?

Barrel is different
Bolt face is different
Mags are different

Are you getting barreled action or just actions?

This may be something you don't want at all.

Actions aren't chambered in anything, so it would be a standard short action and magnum bolt face short action.

Creedmoor and Saum use different mags.

Thanks, all.  I am clearly uninformed on this issue so I am unable to assess value, etc. on a potential deal.

I can seen now that obviously the action, chamber, and barrel are one unit.  Therefore, changing from SAUM to Creedmor in an MPA chassis means changing all of this, which is probably a simple matter of a few allen screws.

Just so we’re clear on terminology the chamber is in the barrel and the barrel screws into the action.