the other point is you use a lot more POWDER for another say maybe 200 yards range- something like another 20 grains, give or take- they use the same bullets,so it's really a question of whether you want the "longer legs"plus the ammo is of course much more expensive because it's got the word "MAGNUM" IN IT- same deal goes for the gun
the way i look at it is this: the 308, 06, and 300 are basically the same, but each has longer legs( ie more range ) and burns more powder to get there. provided you use the same bullets- however, if you're going to go over 220 grains in 30 cal, you might as well go for the 338
you also have to check the twist of each of the 30 cals- the faster the twist , the better it'll handle heavier bullets
308's can be either 1/12 or 1/10, the 06 is typically 1/10 , as is the 300- so both the 06 and the 300 can handle the same "spectrum" of bullets, just that the 300 does it faster