"Slight resistance" is exactly what I found with my rifle, chambered using Nosler/Norma unfired brass, with unfired Remington factory .280 brass.
That said, after some experience with several "improved" rounds, mostly 40-degree Ackleys in cartridges from .223 Remington to .35 Whelen, fired "unimproved" brass in the same chamber often won't even go band, due to the lack of the little shoulder/neck radius on new brass.
My point is that .014" difference in headspace (IF the .280 AI chamber is reamed that accurately) is a very tiny amount--and a very slight amount of variation in both the chamber and brass can work just fine, whether the chamber is supposedly "original" Ackley Improved or Nosler.
