I was surprised when I loaded winchester brass in place of military brass. With military, I used 25.9 grains of 748, and with winchester it took 26.4 grains to get good results. Brass thickness made a significant difference.
Is slightly misleading. Needing 0.5 grain difference in charge weight between brands of brass is very normal within the realm of "commercial" 223 brass.
To put this into perspective this is a 2% difference in charge between the winchester and milsurp brass, this is not anything to get worked up about. Case thickness could be secondary to case hardness (if Winchester were softer it would expand against the chamber walls quicker and give the same "lower pressure" signs as a large case capacity). So, unless you measure with water to be sure that it is in fact case capacity it is nothing to get worked up about.
But whenever you change a component, redo your load work up to ensure safety.