Hi NWshooter69, I believe you are correct about standard Ackley Improved cartridges. My rifle was put together by a bench rest shooter who was a stickler about neck thickness and uniformity. This is why we started with unfired brass and first turned the necks prior to fire forming the case with maybe 5 grains of pistol powder followed by corn meal and a plug of soap (see photo sequence). These cases were then trimmed to length if needed and after removing the primers and expanding the necks they were reloaded with a collet sizing die made by Lee Precision Custom based on two fired brass cases and one loaded bullet from my rifle). My recollection is that standard 220 Swift bullets with standard neck thicknesses either would not chamber in my rifle or if forced would create undue neck pressure which could be dangerous.
I lost all my reloading equipment in Hurricane Ike in 2008 including my dies, neck turners, scales, press, etc. I'm retired now and after checking into the Whidden sizing dies that 1badshee suggested I posted a question about collet vs bushing sizing dies on the reloading forum here on Pred. Masters. Another user suggested it might be cheaper to have this “220 AI variant” rechambered to 22-250 AI which and allow me to fire form commercially available 22-250 rounds as you suggest AI cases are typically formed and then neck size rounds for any subsequent shooting. This sounded like a simpler and safer alternative and I’m looking for gunsmiths in the area that might be able to rechamber the rifle to either 22-250 or 22-250 AI.