T O'Heir,
You are correct, that is what Hodgdon currently lists. I also know for a fact that 22.7gr of IMR4064 is not a compressed charge under 75~80gr match bullets.
Snickering aside, it's good to check multiple sources. The old IMR reloading books from 2005/2006 lists 24.0gr IMR4064 compressed for 75gr bullets, and 22.7gr Compressed for 80gr bullets. In fact the 80gr bullet data is exactly the same for max charges as the 77gr load data for all powders listed except for IMR3031 where the difference is 0.1gr. Also, for the given charges in that old book, the 80gr SMK has lower pressures with the same charge generally means something is screwy with the load book, especially since the 80gr were loaded significantly closer to the lands than the 77gr bullet.
But, you have to understand, before that year IMR didn't list load data for anything heavier than 55gr in 223 Rem, so it makes sense that they recycled the 80gr data they had for the 77gr loads and just hit "publish" and once Hodgdon bought out IMR they just kept publishing the same data.
So looking to the bullet manufacturer... Sierra lists 24.1gr of IMR4064 for a 69gr HPBT and 23.8gr of IMR4064 for an 80gr Boat tail, so right at 24ish grains (23.9 to be precise) is where the calculated max would be.
http://accurateshooter.net/Downloads/sierra223ar.pdf
Then again, Hodgdon lists 24.0 gr of H4895 as max with an 80gr SMK, and Sierra lists only 22.9gr with the same bullet. Go figure.
But powders do change slightly with lots, so do the load workup.
Jimro