I should have added this to my first post but it was late and brevity seemed important at the time.

Some questions are practical and some are academic.   

The first question is practical.  For a given bullet, twist rate is the major determinant of stability.  And, if the bullet is not stable from muzzle to target, nothing else matters; you will not achieve consistent accuracy.

The second question is academic inasmuch as it asks whether or not there is a correlation between twist rate and wind deflection.

For a given bullet, only a very narrow band of twist rates will stabilize that bullet out to 200 yards.  And, as both under and over stabilized bullets are inherently inaccurate, only those twist rates that keep the bullet stable out to 200 yards have any practical significance.

Accordingly, questions regarding the effects of wind on under or over stabilized bullets are interesting, but have little, if any, practical application.

JackHughs

To talk about wind and bullet stability is like talking about apples and oranges.

Keep on hav'n fun!
MikeT

I found out some things today. The Magnus effect results in an asymmetrical distribution of air in the boundary layer of a spinning projectile. The bullet drifts toward the low pressure region of this distribution. That's from the 1935 Ed. of Exterior Ballistics by Lt. Cdr. Ernest Herrmann, USN; Ch. 9 Article 904. He also states that it is a very small effect, but he was discussing much larger projectiles than ours so it is difficult to interpret what he meant by "small".

My thought: The shape of the asymmetrical Magnus distribution would be altered by gusting crosswind. If the low pressure side of the Magnus distribution is upwind the gust would reduce the the effect and if downwind, the opposite would occur. So, a faster spin rate--meaning a more pronounced Magnus effect--would have a greater effect on drift. 

Herrmann states later, in Appendix D, that drift of some projectiles in a direction opposite of that predicted by the Magnus effect has been observed. 

Interesting, but not conclusive.

Dr Tom

IMO, there is no such thing as overstabilization - you just use a heavier bullet.  Understabilization is MUCH worse, and a bullet on the ragged edge of stability might just be sent 'over the edge' by some less-than-ideal wind conditions.  But the bullet was understabilized to start with anyway....
Range also hs something to do with it, as well as MV (don't forget the transition from supersonic to subsonic, which is pretty turbulent).  More drift with a faster twist?  that's just a few clicks on the sights, a minor issue...

How do we know when the bullet is on the ragged edge of stability?
joe b.



MartiniBelgian wrote on Oct 30^th, 2012 at 3:57am:

On the practical side, determining the 'ragged edge' of becoming unstable is easy to observe - the prairie dogs do flips when the bullet is near unstable and the prairie dogs just fall over when the bullet is very stable.

I agree, it is just a crude indication.  But to see one go straight up 6 to 10 feet is more rewarding than ANY other hit.

The bullet will tumble if it is near un-stable.

Contrast the .223 at 300 or 400 yards with a .308 - very stable - pd falls over and you see four feet straight up twitching.



Agree.  We need to publish a series of references on how to calculate bullet stability - compared to another series of experiencs relating stability to accuracy.

And now my pea brain really hurts.   

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