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Ballistic coefficient — how important?

# Ballistic coefficient — how important?

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.

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.
Categories Ammo, Education / Training

### 28 thoughts on “Ballistic coefficient — how important?”

1. BB,
Another variation that seems to concern many people is variability of velocity in a shot string. But, as I recall, you have had some quite accurate groups from pellets that varied velocity more than you would like.
Maybe a high BC does correlate to better groups at 100 yards. As some people that have Phd after their names might say: “There might be a paper in that.” (No way to tell, until after a thorough research study.)
Also – Maybe people only buy high-performance cars that are painted red? I don’t know.
Bill

• Billj,

“Another variation that seems to concern many people is variability of velocity in a shot string.”
As reported by Extreme Spread (ES) or Standard Deviation (SD) for clarity?
The nut of the issue is what is the cause more than the figure. Extreme Spread is useful but Standard Deviation is a more useful bit of information for a shooter.

I have had many different colors on my high performance automobiles…a RADAR/LIDAR detector was the key to collecting fewer Green Stamps (speeding tickets) since i was Irredeemably spoiled by Autobahnen, Autopista, and Autostrada, before returning to the USA. The state of Nevada and Montana were wonderful for a time!

shootski

2. Hummm. . . I had a sporty, bright red Volkswagen Beetle a few years ago. It wasn’t much of a ticket getter. I now drive a brown Honda CRV. No tickets here either. Maybe its the BC of the cars I drive, or maybe the lack of HP, or lack of turbos, or . . . what? Orv.

• HD

I should think that it would be a more likely case that you don’t break the law as often as many others who own ten vehicles. Over time, the law of averages would catch up with you if you did.

I received quite a number of tickets in my “youth” but as the fines increased, I made a choice. I decided to just slow down a bit,,, most of the time.

I don’t remember if I owned any red ones. Maybe that Sunbeam Alpine I had when I got out of the service. But who remembers that long ago (or is sure of their memory when they reach my age)?

Ed

3. You just need higher BC if you are going to shoot 100yards+ distance. Pellets are not designed to be accurate at this distance, you may of course find some which will be. But you will always have to consider the drop, which up certain distance will be very large. It does not matter how your V0 is – the pellet will drop after 50yards anyway, up 70 yards it will become dramatical. Slugs are a very good option – and same story as usuall, you need to check which is the best for your airgun 🙂 I think up to 50 yards the pellet may win the contest. It will not do it at 100yards compared to slug.
The typical 10m flat pellet will have BC like 0.01. Even though they are sometimes extremely accurate up to 30 yards.

• tomek

Excellent observations to always keep in mind.

Deck

4. I haven’t yet tried shooting at distances more than 50-yards. So, I am just asking. It seems to me (from what I have read) that higher velocities relate to a flatter trajectory. A flatter trajectory, seems to me, should probably be beneficial for accuracy at longer distances. This might be more applicable for targets at varying long distances or moving targets. I would think that a flatter trajectory would be desirable for a hunter, for example.
The higher BCs might or might not make enough difference to be a substitute for higher velocity when it comes to keeping the trajectory flat. But if the slug’s terminal velocity (at the target) is higher than it would be with a lower BC, then it seems to me that it would at least be more effective for hunting.
I have also read that the BC varies with velocity, spin rate, etc. So, tuning an airgun for higher BCs with a specific slug means finding the best velocity for that particular slug in that particular gun.
By the way, whenever I see the term slug used I usually think of the slugs available for shotguns.

• Elmer,

Nope! A flatter trajectory has nothing to do with accuracy at longer ranges. Springfield Armory proved that in 1873 with their .45/70 cartridge.

What a flatter trajectory does is reduce the amount of scope adjustment that is necessary at distance.

The BC does vary with velocity.

BB

• Yes, as usual you said it more clearly than I did. I think that the reduced amount of scope adjustment (holdover, etc) would be desirable for a hunter. Especially one that is not proficient at judging the varying distances his target my be at or moving to.

5. I do not see an option available to modify my above reply. I made a typographical error and should have written it instead of if near the end of the first paragraph. I have sometimes seen that option available and sometimes it has actually worked. I am on an iPad (and usually I do use the iPad).

• It appears that there may be some sort of delay before the edit link becomes available. If I wait say 15-minutes then refresh the page, the edit link has appeared (twice this morning). If you corrected my typo, thanks BB!

6. Like Elmer, I also think of shotguns when slugs are mentioned. I prefer to say cast bullets, though today many manufacturers use swaging as this is faster.

Despite many years of target shooting, I am a hunter. Not just that, but I am a long-range hunter. In my youth I never thought of ballistic coefficients, minute of angle, etcetera. My concern was hitting that groundhog in the head at five hundred yards, because if I hit him in the body there would be nothing left to eat.

When hunting deer, it was the same with the exception that because of the thickness of the woods around here the range is reduced to often under one hundred yards. I always tried for a head shot. It did not mess up any meat and more importantly, the deer would drop right there. If a person shoots a deer behind the shoulders, it may run for hundreds of yards. In these thick woods and steep hills, you may not find it.

A secondary reason for my doing head shots is I cannot stand to see an animal suffer. If my projectile passes through its brain, it is dead. No one is about to convince me that shooting an animal behind the shoulders is quick and painless.

Another thing I have learned over the years is you most often have one shot. If you should miss, your quarry is usually gone. This is why my airguns, and my firearms I used to have, are/were mostly either single shot or bolt action. A quick follow up shot provided for with a semi usually ended up being a miss.

One of the airguns I am experimenting with at the moment is the .25 Armada. It is my intent to see what this air rifle will do with “slugs” at one hundred yards, possibly further. I do hope that it will be able to shoot one MOA at that range. If not, it will be moving out of RRHFWA to make room for some other “old gal”. She may move out anyway. You never know. 😉

• RidgeRunner,

You certainly should plan on only one shot to harvest the prey and NOT take the one shot if you aren’t certain of the shot. Headshots are difficult for the typical hunter both from an accuracy standpoint and understanding of expectable head movement prediction. Most hunters want the antlers (Bucks) and just don’t know when to shoot/not shoot. The “safe” behind the shoulder shot has become the go to shot by default.
The advent of silenced airgun hunting has changed my opinion on having only one shot before the prey bolts.
I have dropped deer, in the still of the night on legal culls, within a herd, the rest just stand still for some time looking at the down deer; enough time to reload my single shot and take out at least two more in a few instances. Granted they were Urban/Suburban Bumbies with no hunter experience.

Good shooting with your Armada…i think you will go beyond 150 easily if the barrel is a good one; i actually hope it is an exceptional one and you get to 200 yards and BEYOND.

shootski

• shootski,

I learned a long time ago that no matter how much I chew on them, the racks have no nutritional value and are very tough to boot.

As for what others choose to do, well. I quit hunting in 1985. If I need to hunt again, it will not be for racks.

7. BB, etal-

Discussion of Ballistic Coefficient (BC) in regards to external ballistics and the effects on accuracy would first require an agreement on terms that is usually missing in this blog.

For instance, in BB’s testing of guns and projectiles, he shoots many groups. Some are very precise in that they exhibit very little deviation in impact point from one to another- small groups. Small groups are good but they are not indicative of accuracy despite most on here (including BB) proclaiming the small group to be ‘accurate’.

To simplify- an accurate and precise group would be a cluster of shots closely centered about the ‘X’ ring or the center dot of the targets that BB uses. As BB has mentioned many times, he purposefully does not center his groups on the target in order to preserve his aiming point. BB knows that he can usually adjust the sighing apparatus to move the impact point. This brings us to the next issue of ‘accuracy’.

An accurate shot is when the point of impact (POI) coincides with the point of aim (POA). Once the projectile leaves the muzzle, all sorts of variables come out of the woodwork to defeat the accurate shot. Gravity is a constant and is the main contributor to the parabolic shape of a projectile’s flight. Air resistance (friction) is second and can be readily affected by changing the projectile’s shape- ie, ballistic coefficient (BC). Now, as BB has said, fine, accurate work can be done with low BC projectiles- the round balls of the muzzle loader era, the .45 caliber of the Trapdoor Springfield, etc.

Buuuuuttttt…. Is a higher BC more accurate? Well, let’s look at Camp Perry (Ohio) and the national High Power matches. Most shooters use Mouse Guns (AR15) at the 200, 300 and 600 yard distances. And they use very high BC bullets. If they didn’t work they wouldn’t use them. Of course well built rifles, good wind calls and some experience and practice go a long way, too.

To sum up- at a given distance from the muzzle, time of projectile flight, wind direction and speed all conspire to adversely affect the intended POI. Increased (higher numerical BC) can minimize, not eliminate, the negative influences of the above.

Perhaps a future blog defining precision, accuracy and consistency is in order.

Have a good day.

8. B.B.

Red cars get more speeding tickets because a higher percentage of Porsches and Ferraris are red.
Remember, most Porsche and Ferrari owners do not understand that driving a slow car fast is more fun than driving a fast car slowly. Those drivers want to drive fast….

-Y

9. I believe that the most probable reason behind tuning for the highest BC has been entirely overlooked. It is commonly known in the world of long range firearm shooting that a consistent BC is necessary to reduce vertical dispersion in the groups. It is also known that bullets fly with a greater or lesser degree of instability, which can cause BC variability and reduced BC’s. (Modern Advancements in Long Range Shooting, Volume III, by Bryan Litz, has some excellent information on this topic.)

I suspect that the shooters whom Yogi referenced are actually tuning for stable pellet/slug flight, which is manifested and recognized by consistent, high BC’s, and will reduce vertical dispersion at distance.

Daniel Krebs

I agree with the gist of your reply Daniel which is accurate.

The fly in the ointment is that there is no such thing as BC; it is mostly used in North America and not in the rest of the shooting world.

“BC is a number that can be used as an input for ballistic solvers to predict trajectories. BC is also used as a selling point for long range bullets so due to this marketing use, sometimes BC’s are inflated or skewed by manufacturers to sell more bullets. As a long range shooter who cares about hitting targets, it’s important to understand the basics of BC so you’re not mislead by marketing hype.”
The Berger Bullet Company

If you want more: https://bergerbullets.com/nobsbc/what-is-a-bullet-bc/#:~:text=BC stands for Ballistic Coefficient&text=BC is a number that,manufacturers to sell more bullets.

The fact of the matter is that ballistic coefficient is this formula:

BC = M/Cd • A

BC ballistic coefficient as used in physics
M Mass
Cd coefficient of drag
A cross-sectional area

It gets worse: A coefficient in mathematics is a numerical factor that multiplies a variable. The variable represents an unknown, and the number associated with it is termed the coefficient. When a variable appears alone without a visible coefficient, it is considered to have a coefficient of 1.

shootski

• So, if I understand, BC in an of itself is of little utility. It only matters as an element in an equation with other variables such as when calculating trajectory or energy. Perhaps some of the fascination with BC is it is a variable in the “accuracy equation “ that can be controlled. As a known value it becomes a constant amidst the many other variables a shooter seeks to control (or wishes he could) when using that particular slug/pellet/bullet.

• Remarq,

Yup, to a point. It may help you get on paper at long range if the BC value supplied by the projectile manufacturer is close for your airgun’s performance.
Have you watched Ton setting the distance record for airguns?
https://www.pyramydair.com/blog/2023/09/ton-jones-beats-billy-dixon-a-world-record/
Hmmm…no calculator that i can see on the shooting bench. He probably did use one to estimate the probabilities before driving out there….

BC isn’t the only thing folks calculate:
https://jbmballistics.com/ballistics/calculators/calculators.shtml

Airgun pellets don’t have a good Standard Pellet for modeling like the: G1,….G7 (to name a few) that bullet manufacturers use.

shootski

• Shootski

So,, what determines the coefficient of drag? Does it change with each bullet? I should think it would since the shapes of the projectiles change.

Obviously the change between an airgun bullet and an airgun pellet are of different shapes. The masses could be the same as could the cross sectional area (depending on where you measures each).

I guess what I’m getting at is that, to me, it appears that the coefficient of drag is what determines which projectile of a given weight will be least affected by air resistance.

So how is that determined? (not in a wind tunnel,,,, or is it???)

Ed

• edlee,

In a projectile it can be done in a wind tunnel to get a value for THAT projectile and THOSE conditions.
But…it changes in the barrel and at the muzzle immediately and continuously, and with Yaw, and Relative Wind, and atmospherics, and surface grooves, and spin, and, and.
But i can give you a good Cd when i shoot one projectile and record it with my LabRadar and then do the computational manipulation of the points recorded along the projectiles flight. I can do 5 or more points muzzle to target depending on how long you want to wait. But what do we have then? We still don’t know the WHY. There have been cases where Ballistician have seeming seen bullets stop and actually reverse (briefly) in flight using really expensive Doppler RADARS; turns out it was a case of precession and nutation becoming additive for a RADAR pulse.
Don’t think weight, think MASS.
Don’t think cross-section think Form Factor.
Think negative Acceleration.
In the end i need to use Gunfun1’s targets (paper, steel, fur, or reptile skin) don’t lie.
The rest of this stuff is all computational and model driven.

shootski

PS: if you agree with George E.P. Box you will understand why shootski doesn’t worry about AI taking over successfully. It will never be able to interpret the results well enough.

• Remarq,