A sleek, light hunting bullet can buck wind as well as a blunter, heavier one.
By Ron Spomer
Anyone who has ever pulled the trigger on a Daisy and watched the BB arc and curve toward its target understands wind deflection. The stronger the wind, the farther that BB gets blown off course.
Anyone who has shot beyond 250 yards at game in a 20-mph or stronger wind also understands wind deflection, usually shown as a puff of dust on the downwind side of the target.
And anyone who has gone that far in this shooting game has heard of the common cure for wind deflection: big, heavy bullets driven to super-magnum velocities. Ouch.
Yes, ouch. Recoil is a heavy price to pay for the wind-defying talents of a 200-grain .308 bullet launched at 3,200 fps from a .30-378 Weatherby. Especially when you realize that the big slug isn’t defying the wind, anyway.
The truth is, every projectile is deflected by wind. And you don’t necessarily need a shoulder-numbing magnum to counteract this tendency. Instead, shop for maximum velocity in the highest ballistic coefficient (BC) bullet you can find that provides the terminal performance needed to cleanly take your chosen game.
In some cases, this might be a 250-grain Nosler AccuBond spit by a .338-378 Weatherby at 3,000 fps. But in others, it might be as pleasant as a 140-grain Hornady SST Interlock from a .264 Winchester Magnum at 3,000 fps, or even a 75-grain Swift Scirocco from a .223 Winchester Super Short Magnum at 3,350 fps or something in a .270 or 7mm. There are lots of options for all shooting assignments.
Velocity and aerodynamic efficiency are the keys to minimizing wind deflection, not mass alone. Mass helps maintain inertia (forward motion) and resist forces trying to impart momentum in another direction, but so does shape. A spire-point bullet that slips through the air maintains higher velocity and gets to the target faster than a flat-nose bullet that pushes air ahead of it.
That means there’s less time for wind to act upon it. This is why a 150-grain .308 Sierra Pro-Hunter flat nose with a BC of .226 launched at 3,000 fps from a .30-06 will drift 11 inches at 300 yards in a 10-mph right-angle wind, and a 75-grain .224 Swift Scirocco with a BC of .419 sent flying from a .223 WSSM at the same initial velocity of 3,000 fps will drift just 5.1 inches.
But that’s just part of the story. From a .30-06 (which imparts all the recoil many shooters care to endure on a regular basis), 3,000 fps is top-end velocity for a 150-grain slug. The .223 WSSM, on the other hand, can nudge that 75-grain pill to 3,300 fps or slightly faster. At that speed, it will drift only 4.5 inches at 300 yards.
Does this mean all 75-grain .224 bullets are vastly superior to all 150-grain .308 bullets? Hardly. Remember, it’s the combination of high BC and high velocity that fights wind deflection. Step up to a 150-grain Berger Match Boat Tail with BC of .408, send it flying at 3,000 fps from your .30-06, and at 300 yards it will drift just 5.3 inches, a virtual tie with the 75-grain .224.
The trick for minimizing wind deflection, then — with any cartridge/rifle from the .30-30 Winchester to the 505 Gibbs — is to identify the highest-BC bullet it will fire and then push it to maximum velocity. Stated another way, seek out the longest, sleekest bullets for your caliber. In the .270 Winchester, for instance, the 150-grain bullet with the same nose shape as the 130-grain, 110-grain or 90-grain will “drift” less if all are driven to maximum velocities. The lighter bullets will shoot flatter; the heavier ones will deflect less in wind.
This should give you some ideas. For example, “I wouldn’t have to put up with the recoil of a super-magnum .30 caliber if I could find a smaller caliber that will drive a lighter bullet with the same BC to the same velocity.” Let’s try that.
A search of bullet catalogs in my files uncovers a 208-grain, .308-caliber Hornady A-Max Match bullet with a claimed BC of .648. Nosler claims .588 BC for its 200-grain AccuBond. Berger sets down .631 BC for its 210-grain Match VLD .308. Let’s be optimistic and go with an imaginary 200-grain .308 with a BC of .630. Now, the biggest engine to drive that bullet is the .30-378 Weatherby using 105 grains (almost twice the powder a .30-06 would hold) of Hodgdon Retumbo powder. According to the 2008 Hodgdon Annual Reloading Manual, this combination will yield a muzzle velocity of 3,200 fps. Yowser! Let’s see a pronghorn escape that.
Okay, according to the wind-drift tables in the back of the 6th edition “Hornady Handbook of Cartridge Reloading,” our imaginary bullet will drift just 3 inches in a 10-mph wind at 300 yards. A 20-mph wind would double that to 6 inches. Those are comforting numbers during a Wyoming antelope hunt. The roughly 30 foot-pounds of recoil generated in an 8-pound rifle are not so
Now, let’s see how close we can come to that with a milder rocket. Berger builds a .243 115-grain match VLD it rates at .595 BC and a .264 140-grain Match VLD rated .640. Let’s go with the .264. We’ll need Winchester’s old and often overlooked .264 Magnum to push this baby 3,000 fps by burning 68 grains of H1000. (Some wildcat cartridges might nudge that to 3,200 fps, but we’ll stick with factory cartridges here.) How does this 140-grain .264 WM load match against the .30-378? Well, the Hornady wind drift tables don’t extend to .640 BC, but the .630 BC chart shows our .264 bullet will drift 3.3 inches at 300 yards. We can subtract .2 inch of that to compensate for the extra BC and call it a tie. Hey! My shoulder is feeling better already. Recoil energy from a 140-grain bullet pushed by 68 grains of powder is roughly 17 foot-pounds in an 8-pound rifle. Much nicer.
You can dig up this and similar information from catalogs, reloading manuals or computer ballistics programs such as Sierra Infinity. It’s easier to minimize wind deflection with bigger bullets, but it isn’t impossible to match or nearly match them with select bullets in smaller calibers. If you don’t like recoil, try it.
But remember to consider bullet construction, too. Just because a target bullet sits atop the BC heap, don’t assume it’s going to deliver the kind of terminal performance you’ll need for elk or moose. Many shooters have been reporting dramatic success at extreme ranges with Berger bullets. I’ve had great luck with A-Max and Sierra match bullets at longer ranges, but the manufacturers don’t recommend these for big game, so proceed with caution. It may be prudent to select not the highest BC bullet in any caliber, but the highest BC bullet designed for big game, i.e. the Hornady InterBond, Nosler AccuBond, Swift Scirocco, Barnes TSX, Sierra Pro-Hunter and the like.
Keep in mind that not all claimed BCs are accurate. The BCs of most bullets change depending on velocity. Some exhibit higher BCs at velocities above 3,000 fps, some at speeds below 2,000 fps. Doesn’t seem to be rhyme or reason. Manufacturers settle for a reasonable average when listing BCs. A few fudge their numbers on the high side. Most importantly, each rifle will change average BCs. That’s correct. Some barrels deform bullets more than others, creating extra drag. Some barrels don’t stabilize bullets perfectly, introducing yaw (the nose circles off axis like a poorly thrown football.) All this results in BC performance that doesn’t match neat figures in catalogs.
Use BC numbers as a starting point, then check them at the range. Punch paper on windy days, and you’ll discover exactly how wind deflects
Reprinted from the August 2008 issue of Buckmasters GunHunter Magazine. Subscribe today to have GunHunter delivered to your home.