Volume is volume, capacity is capacity, it doesn't matter what media you use to use, as long as you use the same media. Water is a good media to use for measuring smaller volumes, as it fills the space to nearly 100% if you remember to eliminate any trapped air bubbles.
If you look at the common 6.5mm/.264" bore cartridge hierarchy;
The 6.5x55 has more capacity than the 260.
The 256 Newton has more capacity than the 6.5x55 and the 260.
The 6.5-06 has more capacity than the 256 Newton, 6.5x55, and the 260.
The 6.5-06AI has more capacity than the 6.5-06, 256 Newton, 6.5x55, and 260.
The 264 Win Mag has more capacity than the 6.5-06AI, 6.5-06, 256 Newton, 6.5x55, and 260.
But only the 260, 51mm case, fits well in short actions. If you're going to go with a long action, why not maximize the performance potential by going with a larger/longer case than the 6.5x55?
Remember that "better" is never a subjective measurement, but capacity always is.
JEff
