Fascinating Facts About B.C.

Savvy shooters know that a bullet's B.C. rating gives a solid indication on how efficiently it will resist air drag and get down range with maximum energy, minimum drop and minimum wind deflection. But do you know what determines a bullet's B.C?

Two things: density (weight or mass) and form.

The heavier a bullet, the higher its B.C. Thus a 35-grain Nosler Ballistic Tip Lead Free .224 bullet has a B.C. rating of .201, but a similar size 55-grain Ballistic Tip Varmint, with a lead core, brags a higher, better B.C. of .255. An 80-grain Barnes TAC-XP in .355 has a B.C. of .107 while the similarly shaped 160-grain TAC-XP in .451 sports a B.C. of .133.

The benefits of mass seem obvious. You can see the benefit of form by comparing a puny, little .224-caliber, 75-grain Swift Scirocco against Sierra's heavy, .308-caliber, 150-grain Pro Hunter Round Nose. The lighter Swift bullet is rated B.C. .419. The Sierra slug is rated B.C. .200. In this instance, superior form—the long, slim, pointy shape over the short, fat, blunt shape—makes a huge difference in B.C., more than doubling it.

This puts the lie to the common claim that you need a heavier bullet to beat wind deflection. Launch both these slugs at 3,000 fps in a 10-mph cross wind and see what happens:

75 gr.
100 yards
Impact: 1.5 Energy: 1,275 Drift: 1

200 yards
Impact: 0 Energy: 1,084 Drift: 3.3

300 yards
Impact: -7 Energy 917 Drift: 7

400 yards
Impact: -20 Energy: 772 Drift: 13

150 gr.
100 yards
Impact: 2 Energy: 2,120 Drift: 2

200 yards
Impact: 0 Energy: 1,479 Drift: 7

300 yards
Impact: -10 Energy: 1,002 Drift: 17

400 yards
Impact: -32 Energy: 667 Drift: 32

Now there's an eye opener. The bullet that is two-times heavier is deflected more than twice as much in the wind at all ranges. It drops a bit more, and at 400 yards it's even carrying less energy, despite starting out with nearly twice as much. That's what good ballistic form will do for you.

But look what happens when we match B.C. and velocity in two wildly different cartridges, a little .240 Wthby. Mag. and a .300 Win. Mag. Both will throw bullets of about .500 B.C. at 3,100 fps. The .240 kicks out a 105-grain, .500 B.C. Hornady A-Max. The .300 spits a 180-grain, .495 B.C. A-Max.

105 gr.
100 yards
Impact: 1.3 Energy: 1,960 Drift: 1

200 yards
Impact: 0 Energy: 1,716 Drift: 2.7

300 yards
Impact: -6 Energy: 1,497 Drift: 5.7

400 yards
Impact:-17.6 Energy: 1,302 Drift: 10

180 gr.
100 yards
Impact: 1.3 Energy: 3,355 Drift: 1

200 yards
Impact: 0 Energy: 2,933 Drift: 2.7

300 yards
Impact: -6 Energy: 2,554 Drift: 5.8

400 yards
Impact: -17.6 Energy: 2,219 Drift: 10.2

The biggest take away from this is that by merely matching B.C. and muzzle velocity, all cartridges scribe the same trajectories. Yup. Doesn't matter if you're shooting a .300 Rem. Ultra Mag. or a .22-250 Rem. If bullet B.C. and velocity match, they shoot to the same place. The heavier one just carries more energy.


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