@Alabama556 I believe a properly chambered Ackley chamber
should have .003-,006 crush fit on the parent case. That way you wont run into headspace problems with fireforming.
I have had a .223,22-250, and 243 win AI. All of them closed with "feel or slight resistance" on new factory parent brass. Cases actually shrink in the fireforming process, so I'm not sure what the headspace gauge for the parent cartridge will do for you, or what you are trying to measure.
If it's a datum point to determine how much to bump the shoulder w/ full length sizing... it will probably work.
In addition, besides increased case capacity, the beauty of the PO Ackley design is minimal case growth. Good Luck- I love Ackleys! .