I stand corrected.
The Barloc DOES headspace a 6xc Criterion and Shillen prefit in both the Nucleus and Savage action.
The pic show how much space remains when the barrel is threaded down all the way onto a 6xc cartridge in a Savage action.View attachment 6918947View attachment 6918946
The other pic shows the length of threads on a Criterion. My other Shillen was almost identical.
So I would assume the other Savage Prefit Barrel I have by McGowen would work just fine? Did you cycle the bolt with both those barrels. There was some mention on another thread about some concerns of the extractor or something when cycling on a Savage prefit that was not made just for the Nucleus.