Why is it that the 6.5 bore which is smaller has bullets up to 160 grains but the 270 uses the same weight bullets as the 06. The 06 can shoot heavier bullets and its the same case so why nothing more then 150 grains?
A 6.5 usually come in either a 1:8 or a 1:9 Twist. The 1:8 would probably not be good for a 160 gr Bullet, and it is quite possible the 1:9 twist wouldn't be either. Common Bullets available for 6.5mm are 100, 120, 129, 140 and 160. With the twist rates, few 6.5 rifles can shoot a 160gr very accurately.
A .30-06 was designed to fire somewhere around a 165 gr bullet with standard rifling. The lighter weight bullets need just as much of a different twist than a heavier bullet does. The rate of twist dictates what weight bullets fly the best. In a .30-06 150 to 180 gr are probably most accurate in a majority of rifles produced today, because of the twist. Not many 30-06's are as accurate with either 130 gr or 220 gr ammo. While there are more bullet choices for 30-06, they are not really the most accurate. Some 30-06's have different twist rates, but a majority are produced so 150 to 180 gr bullets perfom best.
Since a 270 usually comes in few twist options, the available weight of bullets is more than likely what is most accurate for the common twist rate that is manufactured. And with the making of 270 Mag's, the bullets may get even lighter, instead of heavier.
