The only really problem with shooting a light for caliber bullet out of a fast for caliber twist is the possibility of making the bullet self destruct enroute to the target. In order to stabilize a bullet of a certain diameter and length, you need to make the bullet spin at or above a certain RPM. This is why a typical .22-250 has a 1:14" twist, while a typical .223 has a 1:12". Shooting the same length bullets at higher velocity requires less rifling pitch to achieve the same desired RPM.

Of course, as bullets get heavier they get longer, which means they must spin faster to be stable. Additionally, for a given cartridge, heavier bullets mean less velocity, which makes even more rifling pitch necessary to achieve the minimum stable rotational speed. The caveat to increasing the rifling pitch to stabilize very long bullets at slower velocities is that when you propel a standard to light for caliber bullet to much higher velocities, the rate of rotation becomes abnormally high. For a hearty bullet like a 55gr NATO ball FMJ, such rotational rates don't effect it at all, but with a thin jacketed varmint bullet designed to disintegrate impact the excessive spin can cause the bullet to expand and fragment in mid-air.

The result is usually a cool grey smoke trail and fragmentation hits on the target.

Mike