I ran the numbers on some of the loads I have, based on consistent chrono results (here: http://jbmballistics.com/cgi-bin/jbmstab-5.1.cgi), and the results were interesting.

The linked site says: “The Miller stability value … should be between 1.3 and 2.0 to ensure stability (the military uses 1.5).”

The most accurate load I have is a CorBon-loaded 225gr TTSX out of my 1:10" .340 Wby at 3,140 fps.

It came out to a stability factor of 2.685—way above the 2.0 max suggested by the link.

What is supposed to be the problem with over-stabilized bullets above 2.0?

None that I see

I don't think there is such a thing as "over-stabilizing" a revolving cylindrical object along its long axis.

An SG value above 1.5 ensures super-stability, which maximizes BC.

The only potential problem with a high SG value is that precision can suffer if the bullet is not perfectly concentric. Today’s bullets are more concentric than they used to be, so the potential difference in precision between a high SG value and a low one, is really only pertinent to BR applications.

Thanks for the insightful comments guys.



Forgive my ignorance, but what do you mean by BC? Not ballistic coefficient I assume.

Indeed he does mean ballistic coefficient.

Okay, so school me on that. Just trying to understand. If the bullet isn't yawing, a faster spin can raise the BC? Or is something else at play here?

The longer the bullet and the higher its BC, the more spin it needs not just to fly straight but to realize its full BC value. Long rifle bullets tend to get more stable as they fly, at least until they get to the trans-sonic velocity range, but bullets that have enough spin to fly nose-forward may still experience a sort of precession in flight before they settle down. This precession significantly reduces the BC value of the bullet. A fully stabilized bullet, according to current ballistics, experiences a minimum of precession due to its spin rate, and thus has a maximized BC based on its shape.

I came to all this stuff by reading the writings of Bryan Litz, a professional ballistician who does some work for Berger along with independent research. I'm trying to simplify what I've gleaned into a few sentences. I hope I didn't confuse further due to not having finished my coffee yet.

This is an interesting subject that takes a lot of digging and thinking to comprehend. I researched it myself to find the answers, and the best search term to use is "tractability." Tractability is the term used to describe the bullet's ability to keep its rotational axis tangent to its trajectory.

It may be true that overspinning a bullet can cause issues when a bullet is not perfectly dimensioned and constructed. The bullet might disintegrate, or simply exhibit degraded accuracy, but this is not the same thing as overstabilization.

A bullet that is tractable in flight keeps its rotational axis tangent to the trajectory and impacts the target [almost] perfectly nose first. An overstabilized bullet is not tractable.



Tractability must be maintained throughout the bullet's flight. If it isn't, the bullet does not fly [almost] perfectly as it begins to descend on its trajectory. If tractability isn't maintained, then it begins to exhibit a slightly nose-up attitude and that would negatively impact its BC at that time and the trajectory becomes no longer predictable. Your dope is no longer valid at that point.

Tractability is a product of the interaction between gyroscopic force and the overturning moment. The overturning moment is produced by the center of pressure caused by aerodynamic resistance, and is constantly trying to disturb the relationship between the path of trajectory and the rotational axis of the bullet in flight, but the gyroscopic force resists the overturning moment. The reason that it works is that the gyroscopic force reacts to the overturning moment by countering it with a 90-degree offset response. During the instant that the overturning moment wants to push the bullet's nose up, the gyroscopic force pushes the nose either to the left or the right, depending on the direction of spin (CW or CCW). It's a constant battle between the two forces. In simplest terms, the overturning moment is always "a day late and a dollar short" but its presence allows the bullet to fly perfectly [almost] nose-first.

I do not know how far you'd have to shoot to see the effects of overstabilization, but I'm pretty sure that it would have to be a lot further than most of us shoot. I am not sure just how fast a rate-of-twist would have to be to induce overstabilization, either. It just doesn't seem to happen to the extent anyone would notice it but it's certainly possible. Somewhere I read about someone experimenting with twist rates as quick as 1:4. Don't ask me where I saw that because I sure as hell couldn't recall.

The reason that too fast a rotation can theoretically exist is that forward velocity degrades much, much faster than rotational velocity. At some point, this would cause the overturning moment to become so weak that it cannot affect the gyroscopic tendency of the bullet to maintain its current attitude. This would mean that the overturning moment would no longer have the ability to force the bullet to correct any discrepancy between the bullet's rotational axis and its trajectory.

Here's an interesting video about the .408 Chey-Tac. I've watched it a few times, and what I get out of it is that having the correct balance between gyroscopic force and overturning moment at the time the bullet encounters the trans-sonic zone is critical in long range shooting. This is not stuff I employ, or ever plan to make use of, but always wanted to understand. I just like to know (when and if I can).

RR: Great explanation of the tractability of bullets. I always referred to it as the bullet going to sleep and this was wrongly applied to why sometimes groups are the same or better at 200-300 yards. It is usually a parallax issue not the bullet wobble settling down or going to sleep.

Back to the OP's question, the slight over stabilization will not be a factor at hunting ranges or possibly not at all. The stability factor in the 1.2-1.5 zone will not cause a loss of accuracy usually, but will cause a loss of BC to varying degrees. The Berger calculator list this.

Overstabilization can cause accuracy issues if the bullet isn't perfectly balanced. As Jordan said, that's usually not a problem with today's bullets. Too much stabilization also means high RPM's so fragile bullets can suffer jacket failure and spin apart. I have a 20 practical with a 1-8 twist that will spin apart 39 gr. sierra blitzkings because of the fast twist, a tougher bullet like the 40 gr. Vmax won't fail. That's also not a factor with a Barnes, you're not going to spin them apart.

As long as they shoot good, don't worry about it.

It's not limited to nose up...
Cross wind affects the bc in a similar (but opposite, I think) manner as gravity.
The wind has greater effect on the center and tail of the projectile causing it to point somewhat in the direction the wind is blowing from.