 Mag.thoroughly eclipsed its popularity has been attributed to many causes, the premature "burning out" of barrels as compared to the Remington cartridge often cited.More likely is the fact that hunters had more confidence in the game-getting ability of heavier 7 mm (.284") 150 to 175 grain spitzer-shaped projectiles on big game, as compared to 140 grains being the upper end of pointed .264 bullets.