Posts Tagged ‘chronographs’
by Tom Gaylord, a.k.a. B.B. Pelletier
This topic was suggested by veteran blog reader Kevin. I liked it because it gives me a chance to say some things to the new airgunners; better yet, it’s a great way to start a discussion among all you readers.
I will touch on the things about chronographs, which are near and dear to me, but I think my role today is simply to get the ball rolling. We have enough readers with chronograph experience that I’m sure they’ll share a lot of their own viewpoints — some of which may never have occurred to me.
What is a chronograph?
The term chronograph means different things to different people. To an horologist, it might mean a particularly accurate instrument (watch or clock) to record the passage of time; but to a shooter, it means an instrument that’s used to measure the velocity of a projectile. It still records the passage of time, but also performs an additional calculation to convert the results into velocity. As incredible as it sounds, we’re able to measure the speed of a pellet or bullet moving hundreds, or even thousands of feet per second with an instrument we can buy for as little as a hundred dollars.
While ballistic chronographs have existed for more than a century, most of that time they were large, cumbersome, very expensive and difficult to use. It wasn’t until the 1960s that the first portable electronic chronographs became available to the common shooter — and even then they were still very costly and hard to use. You had to shoot through paper screens that had tiny wires running though them, and a sensor would detect when the resistance of the screen changed as some of the wires were broken by the bullet. These screens didn’t last very long in a shooting situation and had to be replaced when they could no longer detect the passage of the bullet. Time was wasted when things didn’t go as planned, and buying chronograph screens was an ongoing expense.
The early electronics were also quite troublesome from today’s perspective. They didn’t directly read out the velocity of the bullet. Instead, they registered the time that elapsed between screen one and screen two, detecting the passage of the bullet. And even that wasn’t direct! They did it by illuminating lights in various columns on a panel that the user had to interpret. The user took that number to a table and looked up the velocity. It wasn’t always given as one absolute speed, either. It was often given as a small range of velocities within which the bullet was traveling — like 2,140 to 2,148 feet per second. It was slow, crude and primitive, but it was the best we had at the time. This was also the time when we were using slide rules to solve complex math problems, and we accepted small margins of error when taking a reading.
These early electronic chronographs were also very imprecise by today’s standards. The precision of their internal “clock” was only about 1/10 to 1/40 that of today’s chronographs, so the number they gave…which was a best guess to begin with…was nowhere near as close as what we get from a modern instrument. Still, they gave us numbers, and we were fascinated by them.
When the first direct-reading chronograph (one that displayed the actual velocity of the projectile) came out, it boosted sales worldwide. Then, chronographs were easy enough for the average user. And when the first photo-sensitive sensors (skyscreens) came out, they did away with the expense and frustration of the old paper-and-wire screens. Both these things happened some time in the 1970s, if I remember correctly. That was when the private use of chronographs really took off.
A skyscreen senses the passage of a projectile by detecting the slight drop in light when the shadow of a pellet or bullet in flight passes over the sensor. Since the light source is often the sky, the name skyscreen became common. This is both good and bad. Good because of how easy they are to use, but bad since accuracy depends on how well the screens are lighted — but that’s a different topic. Today, I want to talk about what the availability of chronographs does…both for and to airgunners.
You use a chronograph to establish the velocity at which a pellet is traveling. All well and good. But the first time you actually do it, you’ll probably be awed by what’s happening. Then, one of two things can happen. You can either put aside your awe and get to work or become enraptured by the numbers the machine gives you and lose sight of everything else. I think that’s what Kevin wanted me to talk about when he suggested today’s topic
Problem No. 1: Speed rapture
The user becomes so engrossed in watching the chronograph readout that everything else stops. This once-sane fellow who used to love nothing more than making acorns dance with his pellet rifle now sits slack-jawed in front of his chronograph, watching the screen for the next number to appear. He no longer shoots at targets. He no longer cleans his gun. He just watches that screen. In extreme cases, he invents things to launch, just to see how fast they go. The chronograph has turned a shooter into a nerd. It’s the equivalent of an addition to a social network; and whether you like them or hate them, you’ve all seen what can happen when the network, itself, becomes the sole focus of a person’s attention.
Problem No. 2: Infinite dissatisfaction
The chronograph owner uses his machine to determine how much he likes a certain airgun. Because nothing is ever perfect, he’s never satisfied with anything. His chronograph has become like the magic mirror on the wall — but one with an extreme personality disorder. It spray-paints dissatisfaction on the overpass of his life.
This guy will buy an airgun, then shoot it over the chronograph until it fails to please him. You see, he’s learned that if you do something long enough, eventually you get the results that come from the bad side of the curve. When that happens, it sets off his spring-loaded trigger of dissatisfaction, as in, “I knew this rifle wasn’t as good as they said! And here’s the proof!” As Midas was unable to survive when everything he touched turned to gold, this fellow is in pretty much in the same boat; though, when he touches things, they turn into something far more objectionable.
Problem No. 3: The statistian
This shooter used to be the life of the party until he got his chronograph. He now carries a notebook full of columns of numbers that he will try to work into any conversation. You’ll ask him how things are going, and he’ll whip out a spiral-bound notebook with the numbers he’s collected over the past six months. Somewhere in all that data is the answer to how he’s doing — he just can’t quite put it into words. But he’s got the number to back it up! How’s he doing? Please turn to page 46.
Problem No. 4: Dazzled by the charts
This guy takes his chronograph numbers and creates charts with them. But he’s never taken a statistics course, so he isn’t really sure what the numbers are telling him. But he has found that he can tweak the presentation of the numbers on the charts to make them look any way he wants. For him, happiness lies in finding the best way to make his new airgun look good by adjusting the values on the scales of the charts. He’s really the same as guy No. 2, only his outlook is positive, where No. 2’s outlook is — well — it’s No. 2.
What good are chronographs?
It probably sounds like I’m against the use of chronographs, but that really isn’t the case. However, I do advise using them as tools — not as crutches. For example, do you first find the fastest pellet, then see how accurate it is? Of course not! First, you find the most accurate pellet, then see how fast it goes. If it doesn’t hit what you aim at, its velocity is secondary.
I see the same thing with those who reload centerfire firearm ammunition. They keep searching for the fastest load for a particular gun, with one eye always on the chronograph screen. They seem oblivious to what that cartridge is doing downrange — just as long as it’s the fastest in their gun. They paid for the speed their rifle can deliver, and by gosh, they’re going to get it! It’s akin to being the “fairest in the land,” don’t you think?
I turn this around by never consulting the chronograph until I have the most accurate round. Whether it’s a centerfire cartridge or a pellet, it’s all the same to me. I want to hit my intended target. Once that happens, I get interested in velocity, but only to know how fast the projectile is going — not to tweak it to go faster.
Okay, Edith pointed out that I test velocity before accuracy in my blog tests. That isn’t in contradiction of what I just said, because when I test an airgun here I am seeing what it can do in general terms. In other words, I am looking at power independently of accuracy. But when I test a gun for myself (and spend a LOT longer doing it), I’m interesting in the optimum performance it can give — not in the average performance out of the box.
Chronographs as diagnostic tools
A great use for a chronograph is to test the health of your airgun. If you know how fast it shoots with certain pellets, you can always test it again to see whether anything has changed. I’ve found things like broken mainsprings this way.
You can also use a chronograph to estimate performance of a certain pellet or gun. If, for example, there is an 80 foot-per-second variation in the velocity of a certain pellet in a certain gun, you can be pretty sure that gun will not shoot tight groups with that pellet at long range. They will be elongated on the vertical axis due to the large velocity difference.
Chronographs can also be used to calculate more complex things, such as the ballistic coefficient of a projectile by measuring its velocity at various distances from the muzzle. For this, you need more than one instrument since each projectile must have multiple readings along its flight path.
When I worked at AirForce Airguns, I used a chronograph to test the results of various repair jobs we did to customer guns. Of course, we never knew what the gun was doing before it encountered whatever problem it might have had, but we did know the parameters of a healthy gun. When the rifle was performing within those parameters, it was deemed to be fixed. You may have noticed that I often refer to the Crosman Premier pellet as a “standard candle.” That’s my slang way of saying that I use it in a diagnostic role since I know how fast a healthy AirForce rifle is supposed to shoot it.
There are also numerous other uses for chronographs, such as determining the energy a certain pellet generates, finding the optimum performance curve with a PCP gun and counting the number of useful shots you can get from a CO2 cartridge.
Before there were chronographs, shooters focused on hitting the target. They didn’t talk about velocity — they talked about power, as in, “This pellet rifle is powerful enough to shoot through a one-inch board.” After chronographs became widely available, some people lost sight of why they were shooting and became mesmerized by those alluring numbers.
You know that pellet guns are sold today on the basis of how fast they shoot. There are allusions to accuracy in the advertisements, but the velocity is always given. That’s what the modern chronograph has done to and for airgunning.
Chronographs are wonderful instruments, as long as they stay in their rightful place. Just don’t allow them to take over your shooting life and push the more important things aside.