Originally Posted by
darkker
The answer is about bullet shape and construction. Yes, GENERALLY speaking, longer will be heavier. Now the specifics, from 2 examples. In 223, look at the 77gr. SMK & 75gr. Amax. The Amax is lighter, yet notably longer and needs more RPM to be at the same level of stability. Second example in 308: look at the 150gr. Bullets. The round nose is MUCH shorter than any other shape, from the same weight and mfg.
As for "over-twisting" the weight of the bullet, other than in generality doesn't matter. The jacket is what is the factor. IF the jacket is too thin for the RPM, there becomes a shift in power between centrifugal and centripetal force. Same example of kids on a Merry-go-round. Low RPM and all the kids giggle, to much and they try to get ejected from the center of rotation. If the jacket cannot hold the core together, then like the kids, the core begins to eject from the center of rotation.
The lightly constructed jackets typically talked about, are bullets that were designed for slower twists/velocities from days of old.
Examples are: TNT, SXSP, Dogtown, Varmint nightmare, Hornet bullets.
Those have an RPM limit of approx. 220-240,000. MOST modern varmint bullets are between 290-320,000 RPM