Technical question about twist rates

[Owen Sparks]

We all know that the more aerodynamic a bullet is, the less drag is imposed on it by the air. But even bullets with the highest ballistic coefficient loose a lot of velocity when fired at very distant targets at 500 or 1,000 yards.

This made me wonder, does the rotational spin imparted to a bullet by the rifling slow down at extreme ranges also? Suppose I were to fire a bullet that required a 1 in 10" twist for optimal accuracy. Ar 6 or 8 hundred yards is this bullet still spinning as fast? We know it's velocity has dropped substantially.
Could a bullets spin eventually slow down enough that it becomes unstable in flight and starts to yaw or tumble? Or does the rate of spin slow proportionally with the velocity so that accuracy is unaffected?

Just Curious, OS

 

[USSR]

We all know that the more aerodynamic a bullet is, the less drag is imposed on it by the air. But even bullets with the highest ballistic coefficient loose a lot of velocity when fired at very distant targets at 500 or 1,000 yards.

This made me wonder, does the rotational spin imparted to a bullet by the rifling slow down at extreme ranges also? Suppose I were to fire a bullet that required a 1 in 10" twist for optimal accuracy. Ar 6 or 8 hundred yards is this bullet still spinning as fast? We know it's velocity has dropped substantially.
Could a bullets spin eventually slow down enough that it becomes unstable in flight and starts to yaw or tumble? Or does the rate of spin slow proportionally with the velocity so that accuracy is unaffected?

OS,

While rate of spin does slow down at long range, it DOES NOT slow down proportionally with the slowdown in velocity. If a bullet is fired in a rifle with a slow twist in which the bullet is marginally stable at the muzzle, then, Yes, the rpm's could slow down enough at LR to make the bullet unstable as the velocity drops.

Don

 

[Owen Sparks]

Thanks Don. The reason I wondered about this is I saw some kids playing with a top the other day and was surprised at how long it would stay stable and balanced, at least 30 seconds or more. Certainly longer than a typical bullets flight.

 

[USSR]

There's also some other things that come into play when a bullet slows down at LR. When a bullet goes trans-sonic, bullet design has an impact upon bullet stability. In the case of the Sierra 168 MatchKing, a bullet originally designed for 300 meter shooting, the boattail design is such that it does not handle going trans-sonic well at all. A couple years ago, I was spotting and keeping score for a guy who was shooting these bullets at 1k. The guys in the pits were having a hell of a time telling when this guy had shot and marking his target. I would never use this bullet for LR shooting.

Don

 

[Zak Smith]

If the bullet loses rotational velocity at a slower rate that it loses linear velocity, it should become more stable. (The trans-sonic "upset" may still be enough to cause it to tumble, however.) On the other hand, this same rotational stability can be a drawback if it causes precession and too much variance between the angle of attack and the bullet axis, which may also cause it to go end over end. Comments?

 

[trinydex]

that depends right? if it dropped linear velocity really quickly for some reason i could put hte bullet into an overspin, i have no idea how that would happen but overspin makes wobble right?