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A bullet with a high BC will travel farther than one with a low BC since it will retain more of its initial velocity as it flies downrange from the muzzle, will resist the wind better, and will “shoot flatter” (see external ballistics).[8]When hunting with a rifle, a higher BC is desirable for several reasons. A higher BC results in a flatter trajectory for a given distance, which in turn reduces the effect of errors in estimating the distance to the target. This is particularly important when attempting a clean hit on the vital organs of a game animal. If the target animal is closer than estimated, then the bullet will hit higher than expected. Conversely, if the animal is further than estimated the bullet will hit lower than expected. Such a difference from the point of aim can often make the difference between a clean kill and a wounded animal.This difference in trajectories becomes more critical at longer ranges. For some cartridges, the difference in two bullet designs fired from the same rifle can result in a difference between the two of over 30 cm (1 foot) at 500 meters (550 yards). The difference in impact energy can also be great because kinetic energy depends on the square of the velocity. A bullet with a high BC arrives at the target faster and with more energy than one with a low BC
How do you figure it out
It might be best to let John Barsness explain it:Ballistic coefficient: there's only way to find the bottom of this mysteryby John BarsnessMany handloaders have a touching faith in the listed ballistic coefficient (BC) of their rifle bullets. In fact many choose bullets based on this number, something at least partly the fault of gunwriters, especially many who wrote in the 1960s, when many writers "discovered" technical stuff such as ballistic coefficient and kinetic energy. As an innocent kid, I read lots of articles claiming BC and energy were the truly important things in hunting bullets. It was some time before I gained enough experience to realize many of the writers making that claim hardly ever hunted.They were right about one thing, however: A high BC allows a bullet to shoot flatter and resist wind-drift better, though exactly how much a shooter should worry about these things depends on the shooting involved. BC means just about zilch to a woods hunter, no matter what rifle he carries, but it means a lot more to an open-country hunter or longer-range target shooter.Before World War II discussions of BC were pretty rare in shooting essays, but after the war a whole generation became more technically oriented. Handloading manuals even started publishing the BC's of bullets, though in a rather crude way. I own a copy of the first Speer handloading manual, purchased at a garage sale in Lewistown, Montana. TheBC's listed only go two decimal places. Their 180-grain 30-caliber spitzer, for instance, is listed at .49, a level of imprecision considered inadequate by today's sophisticated bullet junkies.Actually .49 was probably a guess anyway. For many years listed BC's of rifle bullets were arrived at by comparing the bullet to a "form factor," not actual shooting. Other factors were also often involved in such guesses. I have heard through the rifle-loony grapevine that at least one bullet company listed BCs far lower than reality for their boattailed bullets, primarily because the company president hated boattails. At the same time another company, known for their boattailed bullets, listed higher BCs than actual shooting indicated. Similarly, after plastic-tipped boattails became popular, one company made a 7mm bullet with a very high listed BC. A year or two later a competitor brought out a plastic-tipped 7mm of the same weight with a listed BC .001 higher than the first company's.The truth is BC isn't a firm number, like 140 grains of bullet weight. The same bullet's BC varies according to different factors, including velocity. If you go to the Sierra Bullets Web site you'll find a listing of BCs for all their bullets at different velocity levels. For instance, their 150-grain roundnose .308" bullet, meant primarily for the .30-30 Winchester, has a BC of .200 at velocities over 2,700 fps. The BC increases to .227 between 1,700 and 2,700 fps, and to .270 under 1,700 fps.Their 155-grain .308" hollowpoint boattail MatchKing, however, has a listed BC of .417 at velocities over 2,800 fps. This drops to .397 at 1,800 to 2,800 fps, and to .355 at under 1,800 fps. So the effects of velocity on BC are directly opposite in these two bullets.In any such reference, the BC listed is for what's known as Army Standard Metro Environment conditions: sea level, 59 degrees Fahrenheit, 78 percent humidity and a barometric pressure of 29.53. Vary any of those conditions and BC varies as well. Elevation has the biggest effect. The BC of, say, a typical 55-grain plastic-tipped 22-caliber varmint bullet can increase from around .250 at sea level to well over .300 in the Rocky Mountains.I first discovered this myself in reverse many years ago on a trip to West Virginia where a couple of days were spent shooting "ground hogs" (woodchucks) at ranges up to 600 yards. I'd been shooting western rockchucks, another wild marmot, for many years and knew from experience how much bullets drifted in the windier parts of the Wild West. Well, the same bullets drifted a lot more in comparatively mild breezes in the lower, thicker air of West Virginia.Temperature follows elevation in its effect on BC. Colder air is thicker, so 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.
Not to pick our usual fights, but, what do you know without looking up all of your information ? I mean, come on ! People can look that stuff up if they're half smart !
Quote from: CAMPMEAT on May 31, 2012, 06:32:24 PMNot to pick our usual fights, but, what do you know without looking up all of your information ? I mean, come on ! People can look that stuff up if they're half smart !Sure they can, but I know who I trust, and who explains things in a way that's easy to understand. Yes you can Google "ballistic coefficient" and come up with reading material that will take months to read. But I only had to search for "ballistic coefficient barsness" to find what I thought would help the OP the bestest and the mostest. Sorry if I offended you in some way Campmeat.
