The point is each weapon/shooter and combination of components will act differently. As near to being the exact same loadings fired in duplicate weapons will give differing results, sometimes a big difference.
With decent primers and decent new cases, 41 to 42 grains of 4895 or 43 to 44 grains of IMR4064 under a 168 or 175 grain Sierra bullet, if the rifle doesn't shoot 1/2 MOA or better at 100 yards, it's not the ammo's fault. National Match 7.62 NATO and .30-06 loads had the exact same loadings for the entire lot in a given year production. They would shoot much better than 1/2 MOA at 100 yards in thousands of rifles with all sorts of good barrels in them when properly tested by competent shooters.