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one thing the books don't teach is that books are great for theory but don't always work in real life. Once you get below the speed of sound the stability rules change. This is the reason why everyone is suggesting twist rates that seem a bit faster than recommended by millers formula. Also realize that the spin rate of the bullet is directly affected by the velocity and that will affect stability. So now in the real world we use the formula to get in the ball park and testing to dial it in. 1 turn in 10 will not work with the subs and 300gr bullets. Also note that once a bullet tumbles its gone. It won't tumble for the first hundred or two hundred yards and then suddenly be stable. It may wobble or nutate slightly but no tumbling. Many publications have covered the yaw or nutation of a bullet as it clears the muzzle and this behavior is one of the reasons that .223 suppressors are not recommended on barrels less than 10" in length for full auto use.
Overstabilizing is bad for artillery and bad for long distance shooters because the bullet (or shell) nose doesn't tip and follow the trajectory of the projectile. In long range shooting that causes a flow across the projectile which will create drift due to the Magnus effect. It can also cause the fuses on artillery shells to fail due to impacts not being on the nose....newer fuses seem to have made up for a lot of this but it can still happen.
For us in the shorter range world of subsonics none of those overstabilizing issues will really be a problem. Our big worry is overspinning a weak jacket. For the most part I've not seen any issues there either. I've fired 110gr plinkers through my 30-221 with an 8" twist at 2500fps and not blown up the bullet. All of these are the reasons I suggest that over is better than understabilizing.
Frank
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