Re: what change in pwoder in a 223 would make a difference
I used .2 gr increments from 24.0 to 26.2 of 2208 behind a 69 gr SMK when building up a load for F Class. In hindsight this may have been too large a range to cover in a Savage 16FSS [22" barrel]. From my tests [in my rifle] 25.2, 25.4 & 25.6 gr 2208 all had very similar POI versus POA so I have settled on 25.4 gr 2208.
As a generalisation, I have found that the best [most accurate load] is generally towards to upper end of the load window for any given range of data. Consult quite a few sources [eg ADI site, Sierra. Hodgden, Hornady, etc] before settling on the range to test & monitored for pressure signs VERY closely.
Savage 22LR .223 Rem .308 Win