Properly set up, the Headspace gauge used is a Go gauge, minus .004-.006. Go minus .006 is about .010 less than using the No go gauge as the headspace gauge on the AI chamber, which did not work worth a darn in one barrel that I had done this way. He can do the calculations on your action on the headspace gauge protrusion from the back of the barrel. I have used a Redding body die to bump back shoulders on loaded ammo in more than one caliber.
I fire form with 14.6g of Bullseye powder and cream of wheat, and you may forgo the cream of wheat, once fired brass turns out great. Federal brass is soft, don't use it. This method saves you a lot of money and bullets down the barrel. I cool and brush the barrel every 25 rounds.
I like my Ackley chambers set up for a crush fit on the fire-forming case, you will feel slight resistance when closing the bolt. If a case is too tight, I bump the shoulder back just a tad with the full-length sizer....no case stretching.
You can work up a very accurate load for fire forming your brass and hunt with it if you wish.
17 Ackley Hornet, 223 Ackley, 22/250 AI, 6/250 AI, 243 AI, 6 Rem AI, 280 AI were all exceptionally accurate with "forming" loads. I always fire-formed the smaller cases on varmints.
I wish you would forget the "ammo on the shelf" concept, lots of once-fired brass out there in the Winchester brand. If you lose a case now and again, no big deal. A lost case would be where it was work hardened and split at the shoulder with an incomplete fire form, which would be rare unless you used a light fire-forming load with the bullseye.
Forming the cases is nowhere near rocket science.
Tell the gunsmith that he should set up the headspace "tight" on an AI go gauge, NOT loose.