My experience is the same as Tpv's. My 14" .222 Rem would not shoot 55 grain boattails nearly as well as shorter 50 grain flat base bullets. My stability calculator says the boattails were just barely stable (.738" long).
You can download my stability Excel file for a more accurate barrel twist estimate than the Greenhill formula from my file repository, drop.io/unclenick
. The same calculations are available at the online JBM calculators. It is Don Millers revision of the Greenhill to include bullet mass (without knowing its specific gravity), velocity, temperature and barometric pressure conditions. I rigged mine so you can plug in an existing twist as well as a desired stability factor to get the twist result. So far, it has successfully predicted three keyhole events for different shooters. The result is much closer than the old Greenhill formula for velocities from about 1400 fps and up. Below that you are getting into the transonic range and the formula does not have the sophistication to take those quirks into account. My file adds an altitude calculator for barometric temperature and a stability measurement page based on wind deflection diagonal angle.
For your Nosler Partition bullet, I have two lengths. The JBM lengths file says it is 0.790". One of QuickLOAD's two copies of the file also says 0.790" and the other says 0.782". At 3500 fps, my calculator says a 14" twist will not stabilize it. It is close, though.
The way these calculators work is by figuring out the gyroscopic stability factor, s
. When that number is 1 or greater, the bullet is stable. Below 1, it is unstable. My calculator is giving s=0.93 and s=0.96 for those two partition lengths, respectively. That is close enough to be iffy. As a bullet slows down, the spin rate slows much less rapidly, so the stability factor improves after the bullet slows some. I am showing that if the bullet can travel 35 yards without tumbling, it should become stable. That may happen, but given normal velocity and bullet variations, I would not expect it to happen all the time. That's why you can get some bullets tumbling while others don't. This is no recipe for accuracy.
If you want to shoot a 60 grain bullet accurately, Sierra's criterion is not to let the stability factor fall below s
=1.3. At 60 grains, that is 0.700" maximum bullet length. The Hornady 60 grain Soft Point #2270 is that length in my data. If you want a 60 grain bullet just barely stable—say, s=1.05—then you are looking at a maximum length of 0.755". The Norma 62 grain round nose and the 63 grain Sierra semi-spitzer are the two that fit the second criterion of being stable in the 14" twist with little or no safety margin.
Be aware that those stabilities were calculated at 59°C. As it gets colder, the air becomes more dense which increases drag. So the bullet has to spin faster in colder air to resist being overturned by it. That means stability decreases with temperature for a given barrel twist. Frankly, I would not trust either of the latter two bullet choices to be stable below freezing (32°F) from a 14" twist. For that reason, I think the Hornady is the best choice for the weight in that barrel for stability. I would, however, call Hornady to see how tough that bullet is? The online description is the same one they use for the V-max and it talks about explosive expansion. It may only be appropriate for varmints, for that reason? That may also only apply to the V-max? Hornady will tell you.