5 Deer-Bullet Ballistic Coefficient Myths You Still Believe


How Is Your Ballistic Coefficient IQ?

Heavy Bullets Buck Wind

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1 | Heavy Bullets Buck Wind

Many still believe bullet weight alone determines how well bullets resist wind drift — thinking in terms of pushing a box of bricks opposed to one holding linens across a slick floor. The same principles do not apply here, as those boxes are subject to friction from the surface they rest on. The real answer is wind drift is directly tied to flight time; with all bullet weights subject to identical wind push. Simply put, the less time a bullet spends en route, the less time wind has to push it sideways.

How BC factors here is determined by how well bullets maintain downrange velocity. A low-BC bullet (round-nose/short-for-caliber design) sheds velocity/energy faster than one with higher value (long-for-caliber/spear-pointed boat tails). So, though lighter bullets may leave the muzzle at higher velocities, slower bullets with superior BCs can overtake the light/poor-BC projectile given enough distance traveled. Understand this is wholly range related and only factors when shooting beyond, say, 250 to 300 yards. At lesser ranges, differences are negligible.

As an example, let’s use the popular .308 Winchester, paired with three loads pushing 150-grain bullets 2,700 fps from the muzzle — a deadly deer-hunting combination. One bullet is Hornady’s 150-grain Interlock round nose (RN), BC .186. Another is Hornady’s 150-grain Interlock BTSP, BC .349. Finally, Hornady’s 150-grain InterBond boat tail with polymer tip includes a BC of .415. Using Hornady’s ballistic calculator, punching in average atmospheric conditions, 100-yard zero and 10 mph crosswind, the implications become clearer:

  • 150-grain RN: -5.5”/8.4” (200-yard drop/drift) | -21.4”/20.8” (300-yard drop/drift) | -53.3”/40.7” (400-yard drop/drift)                       
  • 150-grain BTSP: -4.3”/4.1” (200-yard drop/drift) | -15.7”/9.6” (300-yard drop/drift) | -35.9”/18.0” (400-yard drop/drift)
  • 150-grain Poly-Tip: -4.1”/3.4” (200-yard drop/drift) | -14.9”/7.9” (300-yard drop/drift) | -33.5”/14.6” (400-yard drop/drift)

Notice how gaps in elevation and especially windage corrections widen as ranges grow longer, the low-BC bullet obviously hemorrhaging velocity past 200 yards, already dropping or pushed out of the vital area by 200 yards, while the higher-BC bullets remain in the vital area with no corrections to nearly 300 yards. The RN is an excellent choice for short-range/brushy scenarios, while the higher BCs widen your margin for error as ranges stretch.

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Light Bullets Always Shoot Flatter

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2 | Light Bullets Always Shoot Flatter

Directly related to myth No. 1, many shooters automatically choose lighter bullets believing they shoot flatter in every situation to create wider margins for error between various ranges within the same cartridge. Returning to our .308 Win, we might select a hot-loaded 130-grain pill breaking the arbitrary 3,000 fps mark, opposed to 165-grain bullets doddering along at 2,600 fps. Speed is addicting, but it’s important to not ignore the bigger picture.

Returning to BC realities — especially as related to viable deer cartridges—you’ll normally find lighter bullets (with lower-BCs), despite higher muzzle velocities, bleed energy faster. Heavier bullets with higher BCs can actually arrive on target at near-identical speeds, but while delivering considerably more energy. At 200 yards, for instance, that 130-grain .308 pill (BC .295) delivers 1,645 foot pounds of kinetic energy to the 165-grain’s (BC .447) 2,220 foot pounds, the 165-grain maintaining 2,043 foot pounds at 300 yards and 1,875 at 400 to the 130-grain bullet’s 1,286 and 991 foot pounds at the same ranges. Meanwhile, velocity differences remain quite insignificant. That retained energy translates into quicker, more humane kills. The heavier bullet also reduces 10 mph wind-drift margins by about 20 percent at 200, 300 and 400 yards.

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Burning More Powder Mitigates Bullet Drop/Wind Drift

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3 | Burning More Powder Mitigates Bullet Drop/Wind Drift

Choosing larger cartridges is commonly employed to minimize drop and wind drift at longer ranges, the reason elk-capable cartridges are commonly found in deer-camp gun racks. On the surface this is basically sound, but applying the physics of BC can often spare you the punishment of added recoil and bluster. I’m not claiming smaller cartridges will always outperform significantly more powerful rounds based on BC alone (though it’s feasible), but I will contend you can produce desired results (and generally shoot better) with something more moderate.

As an example, let’s compare the long-range standby .300 Winchester Magnum and newly-popular 6.5 Creedmoor, both including 200-yard zero and subjected to 10 mph crosswinds. Loaded hot the .300 Win Mag spits generic spitzer soft points (BC .452) at 3,000 fps from the muzzle. The 6.5 Creedmoor launches 140-grain Hornady ELD-Xs (BC .625) at 2,700 fps. At 300 yards the Winchester drops 6.7 and drifts 6.3 inches; at 400 yards dropping 19.4 and drifting 11.6 inches. It also retains 2,301 and 1,963 foot pounds of energy at those ranges. Comparatively, the Creedmoor drops/drifts 7.9/5.2 inches at 300 yards and 22.4/9.4 inches at 400 yards, while maintaining 2,285 and 2,156 foot pounds at those ranges. While the .300 Mag drops slightly less, the Creedmoor drifts slightly less and delivers slightly more energy at the same ranges.

Does all that extra recoil and muzzle blast make sense in light of this information? Moderate cartridges loaded with high-BC bullets — 6.5x55mm Swede (chambered in modern rifles), .260 Remington, 6.5mm-284, 6.5mm-’06, 7mm-08 Remington and 7x57mm Mauser (in modern rifles), even the .308 Winchester or .30-’06 Springfield paired with long-for-caliber bullet, just as examples — make more sense for deer than magnum numbers that punish every time you pull the trigger.

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High BC Bullets Provide Superior Accuracy

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4 | High BC Bullets Provide Superior Accuracy

Intuitive shooters might absorb the information covered so far and conclude high BCs automatically equal greater accuracy. This may prove true at extreme ranges, as velocity lends stability, but is far from universally factual.

First off, long-for-caliber bullets relinquishing the highest BCs typically require faster rifling twist for proper stabilization. Standard 1-in-10-inch rifling twists, for instance, may fail to stabilize longer bullets, eroding accuracy at best, resulting in bullet tumble at worst. Most manufacturers provide conservative rifle-twist recommendations for individual bullets. Over stabilization of light/short bullets is something you’ll hear discussed, but this is old-school thinking, today’s highly-concentric, better-quality bullets making that concern largely moot.

Returning to the original question, BC has no relation to inherent accuracy at average ranges. In fact, many competitive benchrest shooters, directing bullets into tight clusters at 100 or 200 yards, fire flat-base bullets by choice. High BC bullets shoot flatter and buck wind better over the long haul, but this shouldn’t be confused with how well they group at average ranges. My pre-’64 Winchester Model 70 in .30-’06 Springfield, for example, loves 150-grain, flat-base, round-nose pills, sending them into a single ragged hole at 100 yards, while same-weight pointed pills seldom group inside an inch. Rifling twist factors no doubt, but also seating depth in relation to available freebore. Add 200 yards and the streamlined bullets blow the round-nose projectiles out of the water with that rifle.

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Bullet BC Is Etched in Stone

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5 | Bullet BC Is Etched in Stone

Manufacturers generally provide a given BC (often G1 and G7 values), for individual bullets, but these numbers are far from concrete and can even prove deceiving. The reference to G1 and G7 include BC numbers arrived at by comparing established empirical starting points. G1 values were established when cartridges burned black powder and propelled cast-lead bullets, G7 values typically referring to modern, streamlined designs, recorded at much longer ranges. BC also changes with velocity, altered by every inch a projectile travels downrange. Atmospheric conditions also alter BC, cold air more resistant than hot, dry air more resistant than humid, air “thicker” at sea level or with high barometric pressure than higher elevations or low pressure, just as examples.

Manufactures establish advertised BCs using an atmospheric average of, say, sea level with a temperature of 59 degrees F, given common barometric pressure and averaged across a 200-yard journey when shot from cartridges most popular in the caliber of that particular bullet. This is to say published BCs shouldn’t be taken as gospel. For this reason alone it’s important to verify actual impact from your particular rifle/load even after assembling correction cheat sheets using state-of-the-art ballistic calculators (hornady.com and ballistiapp.com, for home computer and smartphone, respectively, are good ones). This makes a chronograph valuable to long-range shooting, establishing true velocities from your own firearm instead of relying on published data. Sierra Bullets also provides BCs adjusted for set velocity parameters.

There was a time when I believed all this BC mumbo-jumbo was an exercise in hair splitting. But as you can see from our .300 Win Mag verses 6.5 Creedmoor example, BC has real-world consequences, especially as ranges began to stretch or when wind stirs. For those who seldom shoot beyond 200 yards, well, not so much.

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Rifle-bullet ballistic coefficients are often misunderstood. And ballistic coefficient (BC) in relation to rifle bullets is the new hotness as more hunters develop long-range aspirations. BC relates to sectional density, a projectile’s length in relation to diameter, and how this dictates how efficiently bullets slip through the atmosphere. Atmospheric resistance affects bullet drop and wind drift most noticeably as ranges move beyond average. For most deer hunters, who rarely shoot beyond 200 yards, BC is a nonfactor, except in extreme cases, such as launching round-nose pills from something like an antiquated .30-30 Winchester or .35 Remington. Yet though BC is a hot topic, many old wives' tales persist. Let’s explore some of these myths as they relate to BC.