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.
What was the headstamp on that military 5.56mm brass?
i've weighed US made 5.56mm and .223 brass cartridge cases since 1968 for my accuracy loads. i've weighed thousands of cases and never found US military 5.56mm cases to be thicker/heavier than US commercial .223 cases.
See brass weights: