ORIGINAL: bigbulls
Yes, I agree that for what ever reason bullet manufacturers tend to make bullets in .264 and .284 diamaters more aerodynamic than any other bullet diameters. I don't know why they do this but they do.
Perhaps because to make the larger calibers as aerodynamic as the smaller ones, it takes a considreably heavier bullet to get the same SD. This would be a requirement if the form factors were identical. This would then add recoil, if these bigger bullets were to be driven to the same velocity levels.... For example, a 160-grain Speer .284 PSPBT has a sectional density of .283, and a B.C. of .556. But their .308 bullet with the same B.C. has a SD of .301, and weighs 200 grains. However, it is a flatbase, (no BT), so it would be a little better if it had a boattail. It could therefore weigh less. Perhaps 190 grains or so.