You will be hard pressed to find .257 caliber bullets with ballistic coefficients that get near .500 or above, if you did your choices would be few. Sure there are some, but they are in weights that are heavy for the caliber and cartridge(i.e. powder capacity) and given that fact, those heavier bullets struggle to retain downrange velocity, thus bullet performance at longer ranges suffers as well. I suppose one could shoot something like the .257 Weatherby Magnum? The 120 grain weights do have good ballistics, but putting your face to the stock of any of Roy's creations is an experience that is likely to make most guys shy away after about the first 5 rounds at the range. The .264/6.5mm caliber has many choices in bullets that easily push a BC of .480 or above, with some that exceed .600, which is really quite high for a small caliber. The 6.5mm diameter just lends itself to making a long, aerodynamic projectile that can be of heavier weight and retain downrange performance yet not so heavy as to need excessive amounts of powder to maintain those downrange velocities, thus the recoil to downrange performance is such that the average shooter will not have to worry as much about flinching and the other issues that come with heavy magnum recoil. 7mm bullets are very good in this department, but the 6.5mm edges them out slightly as well.
