slows bullets down faster. Elmer Keith used to write about holding for 100 yards farther when shooting at longer ranges in cold weather, but he didn't own a chronograph and the powders of his day also tended to lose some oomph down around zero. Colder air does have a definite effect, though.
Many shooters also assume higher humidity also slows a bullet down, when the opposite is true. Hydrogen is a relatively light molecule, so wet air is actually "lighter" than dry air.
Another factor in BC is the yawing a bullet goes through after exiting the muzzle. Early in flight the bullet "precesses" like a clumsily thrown football, but soon stabilizes due to the spin imparted by the rifling. Before the bullet fully stabilizes the BC is naturally lower.
How long the bullet yaws depends on the bullet itself, the rifling twist and even the crown of the barrel. Some barrel/bullet/crown combinations result in a much shorter period of bullet yaw, something apparently impossible to predict. When it does happen, however, the bullet will shoot a lot flatter than indicated in any computer model. A fine example is my .257 Weatherby Magnum, a Vanguard Sporter. This rifle shoots 100-grain Barnes Triple Shock X-Bullets into tiny groups — and also shoots them much flatter than the bullet's listed BC indicates. The muzzle velocity of the rifle's best handload is right around
3,500 fps, and when sighted in 2" high at 100 yards, the little bullet is still around an inch high at 300 yards when shot at typical western elevations of 4,000' to 5000' above sea level, and only 5" low at 400 yards. This is a lot flatter than any ballistic program suggests, even when higher elevation is plugged into the equation.
In fact, so many variables go into what might be termed "effective ballistic coefficient" that the only way to truly find out the long-range trajectory of a particular bullet in your rifle is still to shoot the darn thing. These days BC is often measured rather than computed, especially by the bullet companies whose bullets probably will be used at very long range. Berger Bullets, for instance, has done quite a bit of testing and now claims its listed BCs are accurate within .0005 under Metro Environment conditions. Both Berger and Sierra are great sources of detailed information about BC — but to be really, truly certain where any bullet will land at a certain range and elevation, you simply must shoot them from your rifle. f?I7H
BERGER BULLETS 4275 N. PALM ST., FULLERTON, CA 92835 (714) 447-5456, WWW.BERGERBULLETS.COM
SIERRA BULLETS 1400 WEST HENRY STREET, SEDALIA, MO 65301 (660) 827-6300, WWW.SIERRABULLETS.COM
In the world of revolvers, this gun can only be described with one word - innovative."
Combat Handguns, June 2009 (Dennis Adier)
"That gun had what could be called a perfect trigger pull for a pocket revolver; a smooth and light double action."
Gunblast.com, January 14,2009 (Jeff Quinn)
©2009 Sturm, Ruger & Co., Inc. UJUJIU. RUCER. COM/LCR
Was this article helpful?