I always figured velocity potential was roughly proportional to sectional density in a case with a given capacity. For example, a .25-06 will drive a bullet to the same velocity as a .270 will, given equivalent sectional densities of the bullets used in each. They'd likely require different powders to make it happen, though. In comparing .270 to .280, though, there's not enough difference in bore diameter to make powder choice a significant factor.

Don't be the darkness.

America will perish while those who should be standing guard are satisfying their lusts.