Guys,
What we're talking about here is what works in one rifle, not a universally applied yardstick.
Having said that, I can tell you that I have loaded for 5 223 rifles that I have personally owned plus one other, owned by my hunting partner Craig W. At one point I was loading for 4 223s, so I was F/L sizing and had standardized on one load that, believe it or not, shoots MOA or better in all 6 rifles. This is a near max load using 50 grain vmax (or ballistic tip) bullets and 24.5 grains of AA2230, in WW or Rem cases, with 7-1/2 BR primers. I buy powder in kegs, buying 4 kegs of one lot at a time. I'm now using surplus powder that is very close to AA2230 in burning rate, I believe my present lot is 5% faster than the AA2230; so I am using a bit less than 24.5 grains.
For 40 grain bullets I increase the charge by 1 grain. In Military cases, I reduce the charge by 10%. I do not mix headstamps.
I also prep new cases by sizing, trimming to min length, and removing the burr on the flash hole. This last step is very important, in my experience. After you have done a few hundred cases you'll be amazed at the varience--some cases will have little or no burr to remove--some will have LOTS. You can bet that a case with one of those big bugger burrs will throw a shot way outta your group.
It is my belief that of all the variables involved in making ammo, the powder charge is the most forgiving. Once you find what works things like concentricity and that pesky burr will have a greater effect on group size and consistent accuracy than a few tenths of a grain of powder, especially in the larger cases.
JMHO, of course.