Each of these bullets has a different ballistic coefficient.
This report covers:
- Who cares?
- Definition
- What does BC do?
- Last comment
I was set to write a different report today, but reader Yogi asked a question yesterday that drove me to this one. Here is what he asked.
“Guys at the range tune for highest BC. They have one of those fancy cronies that tell you everything.”
“Is highest BC the most accurate at distance? Is this the proper rabbit hole to climb down?”
To answer that question I will ask you a question of my own. Are red cars faster than cars of all other car colors?
Of course not, you say. Why would you ask that?
Well, because red cars receive the second-highest number of speeding tickets, though only five percent of all cars are red.
According to the National Motorists’ Association, white-colored vehicles get pulled over the most. That said, red vehicles come in second, followed closely by gray and silver.
Unsurprisingly, more white cars are stopped by law enforcement because white is the most common car color. About 35 percent of all vehicles on the road are white. And although red comes in second for the most-pulled-over car colors, only about 5 percent of all vehicles on the roadway are red. So, from a per-capita standpoint, a red car is the most likely to get a ticket for speeding.
What does a car’s color have to do with how fast it goes?Nothing.
What does the ballistic coefficient (BC) of a pellet have to do with its accuracy? Also nothing.
Who cares?
Airgunners who shoot at long range care. They want a higher BC.
Oh, now I get it, you say. A higher ballistic coefficient makes a pellet more accurate at long range?
It doesn’t do that, either.
Then what is it and why do airgunners talk about it so much?
Definition
Ballistic coefficient (BC) is the measure of a ballistic projectile’s ability to overcome air resistance in flight. It’s stated as a decimal fraction smaller than one. When diabolo pellets are discussed, the BCs are very low numbers in the 0.010 to 0.045 range because diabolos are purposely designed to slow down in the air. Their wasp waists, flared skirts and hollow tails all contribute to very high drag that rapidly slows them down — much like a badminton birdie. Lead bullets, in contrast, have BCs between 0.150 and 0.450.
The new airgun slugs that are coming to market have BCs that are higher than diabolo pellets but lower than most conventional firearm bullets. And, by the way — this is why I am so insistent in calling diabolo pellets what they are and bullets what they are. Calling bullets pellets just because they are shot in airguns confuses the discussion. The title slugs is a good one for airgun projectiles that are bullet-like.
What does BC do?
As a result of overcoming air resistance, the projectile with the higher BC slips through the air better (retains velocity better) than a projectile of the same weight whose BC is lower. The rate of slowdown in flight is lower when the BC is higher. That fact exposes the projectile to less influence from the wind.
In dead still air this is of little consequence. But when the wind is blowing even a little, a higher BC means the projectile will move less than one of a similar weight and a lower BC. And that matters in long-range shooting. That, Yogi, is why your airgun friends are tuning for the highest BC. They are tuning their airguns for accuracy at long range. No 10-meter target shooter would give a second thought to BC. It’s only for long-distance shooting.
Last comment
Yogi — do you remember 45Bravo’s report about tuning his Avenge-X Tactical for accuracy at 100 yards? The title of that report was, Air Venturi Avenge-X Tactical slug test. He mentioned that he had been testing his rifle at 100 yards indoors, which is something that most shooters can’t do. His “problem” was when he moved outdoors where the wind is almost always moving, his accuracy suffered. This is exactly where a higher BC comes into play.
So, yes, a higher BC can result in greater accuracy under specific conditions. But BC by itself has very little to do with accuracy.
Tom Gaylord (B.B. Pelletier)
Tom Gaylord, also known as B.B. Pelletier, provides expert insights to airgunners all over the world on behalf of Pyramyd AIR. He has earned the title The Godfather of Airguns™ for his contributions to the industry, spending many years with AirForce Airguns and starting magazines dedicated to the sport such as Airgun Illustrated.
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