mickb wrote:Gents wondering if a 230 grain jacketed bullet out of a 5" 45 ACP with 1: 16" twist that stabilises nicely, will still stabilise if pushed 1500fps out of a rifle length barrel, same twist? Or will the high RPM for such a short bullet be over stabilising it by then and deteriorating groups?
I know there are a couple of formulas to calculate this, and also guys who know this stuff back to front( which I dont).
In my opinion just shoot them and don't think about it too much.
There is no such state for a firearm projectile, which is simply an unconstrained gyroscope, of being 'over stabilised'.
Gyroscopic Stability (GS) can be calculated and expressed as a number such that where GS<1 then unstable and where GS>1 then stable.
The sweet spot is where GS is around 1.5 for the entire flight of the projectile.
At perhaps GS>3 the projectile tends to remain in the exact same plane as it left the barrel which results in a diminished apparent BC at longer ranges due to the projectile not tipping to conform to the slope of the trajectory. Put simply the projectile does not travel point first for the whole of it's flight so is subjected to greater drag making it's BC appear worse than it could be.
Important for long range shooting, meaningless for pistol caliber trajectories, even out of a rifle.