What is a Ballistic Coefficient?

Hunting, shooting or competition, you already know your gear can make or break your day and your accuracy. One major component to figuring out how to hit what you’re aiming at.

But what is a ballistic coefficient? What BC value should you look for? How do you use this number on the back of your box of ammo to ring steel or down a deer at a given range? What’s the difference between a G1and G7 BC?

competitive shooting aiming rifle while in a prone position

Understanding Ballistic Coefficient

Ballistic coefficient (BC) is a crucial factor in determining how your bullet performs downrange. Given the same muzzle velocity and environmental conditions, a higher BC bullet will resist air drag better than a lower BC bullet - giving less drop, better wind deflection and more retained energy at any range.

A function of a bullet’s construction, a BC value can increase or decrease based on the projectile’s shape and weight. This makes common sense – a narrow, heavy bullet with a sleek shape and tip will fly smoother and resist being pushed around by wind better compared to a blocky, light bullet with a flat nose and a non-aerodynamic shape getting blown off target.

The more aerodynamic bullet in the example above would have a higher BC value (closer to 1.0) – than the less graceful bullet. And the higher the BC, the more efficient your bullet is in flight and the better (or flatter) your trajectory will be.

Formally calculated based on the bullet's mass, drag coefficient and sectional density, ballistic coefficient values are a way to compare one bullet to another as we’ve already seen - and a vital piece of info needed to create a ballistic chart of your load.

A bullet’s BC is calculated via a mathematical formula where:

BC = m / d2 i

m = mass of bullet

d = diameter of bullet

i = coefficient of form

How to use Ballistic Coefficient

Unless you’re a math major with way too much time on your hands, you’ll use your BC value to predict your bullet’s trajectory. Using the BC given by the bullet’s manufacturer, plug your G1 or G7 value into your ballistic app or online ballistic calculator along with other data about your load like muzzle velocity, bullet grain weight and environmental conditions to generate a ballistic table.

A ballistic table shows your specific load’s drop, wind drift, and retained velocity and energy downrange, all useful info for seeing what your bullet is supposed to be doing to 1,000 yards and beyond.

For example, here’s a trajectory chart for Premier Match 223 Remington, a factory match-load shooting a 77 grain Sierra Matchking bullet with a G1 BC of .362 and a muzzle velocity of 2,790 FPS.

a ballistic chart showing ballistic coefficient

Ballistic Coefficients Compared

So, does BC really make a difference? How does a bullet with a higher BC help you be more accurate downrange?

Let’s take a 6.5 Creedmoor cartridge loaded with a modern 140-grain match style bullet with a BC of .645 and compare its performance to a 6.5 Creedmoor loaded with an older-style, 140-grain soft point bullet, BC of .390.

Comparing apples to apples, we’ll assume the same environment with a 10-MPH wind, a rifle zeroed at 200 yards, and both loads exiting the muzzle at 2,675 FPS.

	Velocity	Wind Drift	Drop
400 yards	.645 BC 2148 .390 BC 1838	.645 BC 9.2 .390 BC 16.2	.645 BC -22.8 .390 BC -26.6
600 yards	.645 BC 1908 .390 BC 1495	.645 BC 21.6 .390 BC 40.7	.645 BC -75.4 .390 BC -95.5
800 yards	.645 BC 1688 .390 BC 1224	.645 BC 41.3 .390 BC 79.5	.645 BC-167.5 .390 BC -228.5
1000 yards	.645 BC 1488 .390 BC 1050	.645 BC 68.4 .390 BC 133.8	.645 BC -308.2 .390 BC -457.4

As you can see, the longer the range you’re shooting at, the more apparent it is a higher BC bullet assists in staying on target. For example, at 600 yards downrange, the higher BC bullet drops 20” less than the lower BC bullet, with about 19” less wind drift and over 400 FPS more retained velocity. Shooting, hunting, or plinking, this example shows a higher BC bullet makes your job a heck of a lot easier.

G1 vs G7 BC

Now we know how to use BC…but wait a minute, why are there two BC numbers on that box of ammo you bought?

Almost all ballistic coefficient numbers disclosed by ammo makers like Federal, Remington, Speer, Sierra, Berger, Barnes or Hornady list a G1 value. This is an older standard of BC designed to give a standard unit of measurement to flat based, round nosed bullets common in the 19th and 20th century.

More recently, a newer G7 standard has been established to better measure the characteristics of modern, sleek bullets. Today’s projectiles use features like boat tails and long noses with steep angles to improve the bullet’s aerodynamic efficiency and hence BC.

Assuming you’re choosing between two modern, sleek hunting or match bullets. Comparing the G7 numbers of each bullet is the best place to start. You’d never want to compare a G1 to a G7 BC as they are not equivalent measurements – apples to oranges.

While G7 is a “better” BC and generally a more accurate standard to use for today’s bullets, G1 is still a very common way to gauge efficiency and a good starting point for your calculations.

Does BC Really Matter?

rifle on a tripod sitting outside next to binoculars

So, the higher the BC the better right? Why doesn’t every shooter and hunter only choose extremely high BC bullets?

If your lightning-fast bullet gets to 800 yards in a nanosecond but doesn’t expand to put enough energy into that elk you just shot to bring him down, both you and the bull are having a bad day.

Likewise, if you picked the highest BC bullet made by God or man and your local 3-gun match only shoots to 200 yards, your high-end BC won’t make much of a difference to your score.

Bullet construction matters. As with all bullet selection, you should choose the right tool for the job. BC varies based on velocity and shouldn’t be used as the only criteria for picking your next hunting or match load. As you shoot and compete at longer ranges, BC begins to matter more but isn’t the end-all be-all measurement of a bullet.

Understanding and utilizing your BC is essential for shooters or hunters looking to achieve optimal accuracy and performance over extended ranges.