What is wrong with this 223 Rem load?

Four different sources list a maximum load of 25.0 (1), 25.3 (1) and 27.0 (2) grains of H335 with a 55 gr bullet. Start 10% under maximum and move up or down from there. H20 case capacity and OAL seem to be the two biggest variables when it comes to pressure, along with the powder charge. Am I wrong?
Yes, also chamber dimensions will affect pressure.
 
I just went through that a few days ago - comparing nny brass to PPU brass - should be the same? or not? I weighed out 5 of each, dry, with fired primer - to the nearest 0.1 grain. Full Length resized all 10 - then filled each to brim of case neck with water - and re-weighed. Gotta dig out the stats books to find out what I got - single heaviest dry case was an nny (was not the longest); single lightest dry case was a PPU (was not the shortest) - min to max water weight within each group of 5, was greater than difference of average one group to the other group - are they the same to each other, or are they different?? Somewhere, back in the day, I used to be able to do the math about what is a statistically significant number for a sample of 5, but that has gone away - going to have to revisit those books, if I can find them!!!
 
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