It's actually faster twist allows heavier bullets. 1-7 is of course faster than 1-8.
They say 1-8 will shoot the 80 grn bullets, surely will shoot the 75's and 77's. I've got a 1-8 and it even shoots the 60's very well (just started load development, haven't tried a whole lot of combinations yet) but it also shoots the 77's and 69's in factory ammo, but best groups so far (for unknown reasons) have been with 60's, both factory and handloads.
Short range benchresters will often shoot the slowest twist that will still stabilize. They believe that staying on the low end (slow to fast) gives best precision and smallest groups.
A disadvantage of using too fast of a twist is excessive torque when fireing. Which does affect group size and ability to spot ones shots. Excessive torque moves the rifle more when we shoot, so returning the gun to the same exact hold is a little tougher.
Light weight thin jacket bullets can be overstabilized in a fast twist and actually "come apart" at high velocities. There is also a ballistic theory that an over stabilized bullet doesn't fly quite right, but I don't pretend to understand the how and why of that one..........one the other hand, an understabilized bullet doesn't fly at all, it will kinda tumble/wobble and keyhole on target.
