MD has pointed out that either Lapua or VV has published some "modern" loads for the x55 that give it a little more sauce than the .260.
OK, but case capacity doesn't change radically, there is still only about a 4 grain difference. 4 grains is about 7%, so if you apply MD's 4-1 ROT, a 7% increase in case capacity should gain about a 1.75% increase in MV, assuming that all other variable factors remain constant. Therefore, if the 260 is getting a MV of 3,000 fps from a particular combination of components, a 6.5x55 would project to get a MV in the neighborhood of 3,053 fps. Even if a shoot got 100 fps of additional MV, how often is that sort of increase going to make a meaningful difference either in the field or on the range?
