There is another often overlooked relationship that has revealed itself to me of late. That is the relationship of bullet length to balance point of the bullet on its longitude plane. I have recently learned that it is not bullet length alone that determines the rotational velocity required to stabilize a bullet in flight but to some small degree the balance point of the bullet.
Bullets with the balance point farther forward seem to require less rotational velocity to remain stable in flight than do bullets with the balance point farther to the rear.
Think about bullets that depend totally on bullet form for stability in flight without any spin. This type of form stabilized bullets such as hollow base bullets for muzzle loaders with very slow twist rifling and hollow base slugs for smooth bores.
Another example of shifting the balance point of a bullet to enhance in flight stability is with arsenal bullet designs for black powder cartridges such as the 45-70 and 50-70 government cartridges. The 45-405 and 500gn bullets as well as the 50-450gn bullets had shallow hollow base the sole purpose of which was to shift the balance point forward . It is commonly believed that these small hollow base cavities were to promote obturation of the base but that is a misconception because the shape, diameter, and depth of the cavities do little to promote base obturation. Base obturation was achieved through bullet alloy hardness (BHN) and the fast ignition of black powder.
An example of bullet balance point aiding in bullet stability that has shown itself to me is with a 22 hornet rifle with 1/16" twist and two bullet molds each producing bullets of the same length but each having a different balance point due to bullet shape. The design of these two molds that has its balance point closer to the front shoots wonderfully well from the 1/6" twist barrel at all velocities from 1500 to 2200 fps. This is a Loverin type design with very shot ogive so the balance point is close to center but slightly rear. The second design is a bore rider type design that has its balance point farther to the rear than does the Loverin design. The bore rider shows some sign of tipping at lower velocities but shoots reasonably well at the higher velocities.
The loverin design averages better groups than the bore rider both at the higher velocities but that could just be a quirk of the gun that it simply prefers one over the other. This example though has caused me to think a bit on bullet balance and accuracy so that it has now become another point of concern when developing accuracy loads. All of what I have related here is applied to cast bullet use especially in older guns that often used minimal twist rates and were intended to use cast lead alloy bullets.