Don't forget the very high sectional density of the heavier 6.5mm bullets. The only bullets with sectional densities as high as or higher than 6.5 mm's are .338's and 8mm's. These bullets can penetrate carcasses far better than one would imagine for such a modest looking cartridge. AT any range, the a .243 bullet could have more velocity, but a 6.5 mm bullet would still have better terminal performance.