 This is due both to the higher muzzle velocity of the magnum compared to the Springfield and that .284 diameter bullets tend to have better ballistic coefficients than .308 diameter bullets of comparable mass.Because of the smaller bullet diameter .284 diameter also have higher sectional density than .308 diameter bullets, and because of that better penetration in the target (it takes a 206 grain .308 diameter bullet to get the same sectional density as a 175 grain .284 bullet, an increased weight that requires 15-20% more muzzle energy to get the same muzzle velocity).The heaviest commercially loaded ammo available for the 7mm is 180 grains, while the .30-06 Springfield can be loaded with bullets up to 220 grains, but for a .308 caliber to equal the flat trajectory and penetration of a .284 diameter 180 grain bullet with a muzzle velocity of 2,860 ft/sec, as offered for the 7mm Remington Magnum, requires muzzle energy close to what the .300 Winchester Magnum can offer, i.e.