The US military has decided that a Sg = 1.5 is adequate. The Miller Sg estimator has been used & accepted for decades. Looking at the Berger stability calculator:
Should the bullet of choice be the 88 grain 6mm flat base Berger a 9 twist would be required to achieve a Sg greater than 1.5 at sea level at 75 F..
The Berger Sg estimator uses the Miller method and Sg = 1.34 was calculated with a 10 twist & Sg = 1.65 with a 9 twist. The Berger manual specifies a 10 or faster twist for the 88 flat base. On a hot day at a mile high elevation a 10 twist would be more than adequate.
Berger Sg values of 1.34 (10T) & 1.65 (9T) correspond with my Open Office spread sheet derived Sg values 1.34 (10T) & 1.65 (9T) using a barometric pressure of 29.92 inches of Hg, @ 75 F for all calculations.
Plastic tip bullets like the 87 Vmax & 80 Nosler BT achieve adequate stability with slower twists than equal length hollow point, FMJ, or soft point bullets., The plastic tip is regarded as weightless and the tip length is subtracted from the bullet OAL in the Sg estimate calculation.
As mentioned radial bullet density variation due to voids, jacket thickness/imperfections jacket land engraving when subjected to high centrifugal/RPM forces will affect accuracy due to variations of moment of rotational inertia. An example would be selection of slow twist barrels for short stubby bullets used for bench rest competition. Crazy high RPM's & huge Sg values don't correspond with good accuracy.
Should the OP desire high velocity loads giving extended point blank ranges on small targets combined with destructive expansion (splat effect) plastic pointed bullets in the 75 to 87 grain weight would work best. A 10 twist will provide "comfortable stability" for these bullets.
Most of my missed shots are wind caused. When shooting rodents I wait until they are lying flat and then go for the up-wind end. High velocities extend point blank ranges on short targets. The 87 Vmax is my bullet of choice & a 10 twist is optimum for that bullet. The 75 Vmax from a 12 twist would shoot flatter at most practical ranges, about 3700 fps but not as good in wind as the 87 Vmax.
The 95 grain Berger VLD has a very low G7 form factor and with a 8 twist at 3200 fps would be flat shooting but expansion would be lacking. Hornady is expected to produce a low form factor 80 grain 6mm bullet having a low SD and relatively high G7 BC - (SD/BC) and should be good with an 8 twist. They will be pricy at about $0.40 each. These might be a good companion bullet for the 105's that I shoot out of my 8 twist rifles.
Current marketing efforts push long skinny bullets having much weight for diameter needing fast twist barrels. These long skinny bullets having high G7 BC's might not work out so well for shooting rodents and such for practical ranges considering trajectory, recoil, price, & ricochet potential. I would use my 8 twist with a 105 VLD or 108 ELDM for shooting a rodent at 1,000 on a breezy day.
