I posted this in the FCWC section of the forum but thought it would be of interest to all, so have copied my post here as well for discussion.
The April edition of Target Shooter has a very interesting article on BC and bullet stability. It seems the Miller Twist Formula that most of us use for calculating the barrel twist rate required for bullet stability has been verified through testing to be accurate to within 5%.
The accuracy of the Miller formula was never really trusted to be this accurate so a large Sg >= 1.4 was regarded as best practice. This can now be safely reduced to Sg >= 1.3. No more requirement to over spin the projectile in fast twist barrels just to play safe.
The other interesting finding is that tests showed an increase in BC at approx Sg = 1.23. It would be risky to attempt a barrel to achieve this but an interesting finding just the same.
The final bit of info gleaned from this article is that the Miller Formula under estimates the Sg for plastic tipped and open air tipped match bullets as the formula assumes a solid density. This means for most of us shooting match bullets, that the Sg calculated is actually lower than it really is for the bullet.
Using the revised Sg = 1.3 for future calculations may well see many shooters ordering a slower twist barrel that may produce a little more velocity thru decreased frictional forces. Food for thought!
Article is here: http://www.targetshooter.co.uk/april-13-issue.html
Ian
New Info On Bullet Stability & BC
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