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Who needs a chronograph? (August 2006)

by Tom Gaylord
exclusively for © Copyright 2006 All Rights Reserved

The red Alpha Chrony on the right has the skyscreen diffusers mounted. The blue Beta Chrony does not. The instrument can be used with or without the diffusers, which are for bright sunny days.

All Chronys will mount on a camera tripod. This is the easiest way to carry them to the field.

As it turns out - YOU probably need a chronograph more than you know! Airgunners own more chronographs than any other group in the shooting sports. We own them because we can use them much more often. Who can go down to the basement and shoot a few .300 Win Mag rounds while supper's heating? You can shoot rimfire indoors, but it helps if you're not married.

But, a string of 20 shots from a quiet FX Black Widow or Talon SS isn't going to bother anyone, especially if the SS is dialed way down. Or, better yet, if it has the new AirForce Micro-Meter tank attached, nobody upstairs will even know you're shooting anything!

What IS a chronograph?
There are several definitions for the word chronograph, but the kind we are looking at measures the speed of projectiles in flight. Whether they are bullets, arrows, pellets, BBs or rocks shot from a slingshot - as long as they pass through the chronograph sensors, their velocity will be calculated.

What IS a Shooting Chrony?
Shooting Chrony is a brand of chronograph that offers a lot of performance for very little money. It's perfect for the average shooter who wants to know more about his guns. And, the Chrony brand can grow in capability when you're ready for it. We are looking at the Alpha model Chrony that's the most popular among airgunners. It has all the features you need to get started, but it doesn't waste a dime of your money. It records a string of up to 32 shots. It performs the basic statistical analysis shooters need, such as:

  • Average velocity
  • Fastest shot
  • Slowest shot
  • Standard deviation
  • When the Alpha is turned off, all saved data is erased. If you need a machine with a memory, get the Beta model Chrony, which can remember up to 60 shots even when turned off.

    Looking straight down on the first skyscreen, we see a slot at the bottom of the picture. The light sensor is beneath a clear plastic cover. Notice how simple the inside of this Alpha Chrony looks!

    The Chrony is powered by a 9-volt alkaline battery. It is very important to use an alkaline battery, because the sensitive electronics inside the chronograph need the controlled power output of this type of battery. The Chrony is housed in an aluminum box that folds up for transport. You can leave the battery installed, because the unit has a power switch.

    What NOT to do with a chronograph!
    Some shooters get a chronograph and start chrongraphing all their airguns immediately. People who were once happy shooters now stare at the chronograph screen trying to decide how they should feel about the numbers. A chronograph is to airgunners what a fish scale is to fishermen, and some folks are better off not knowing!

    What TO DO with a chronograph!
    There are LOADS of important things you can do with a chronograph. Here are just a few.

    1. If you know how fast your airguns shoot a certain pellet, you will know when they have lost performance and need attention.\
    2. You can check out those inflated advertising claims made by some manufacturers.
    3. You can determine the optimum pressure limits for all your precharged air rifles. For example, the AirForce Condor is very sensitive to overfilling. With a chronograph you can determine the exact top fill pressure your gun will tolerate by filling to 3,000 psi and shooting until your gun starts performing its best. By refilling at that point, you will notice the pressure at which the air tank starts accepting the fill, and that pressure is your maximum fill! Anything higher just wastes air.
    4. In conjunction with reason No. 3, you can calibrate the pressure gauges of all your refill devices. Instead of blindly filling every gun to 3,000 psi, you can discover the exact pressure reading at which each of your airguns develops its greatest power. It won't matter whether the gauge is off by a little bit - you'll know what it should say for the best results with each airgun.
    5. You can check the health of all your multi-pump pneumatics. A chronograph will tell you if your gun shoots faster or slower with the maximum number of pump strokes. No sense doing more work for less results! For example, a Sheridan Blue Streak should develop close to 675 f.p.s. with a 14.3-grain pellet on eight pumps of air - the maximum. If your gun stops at 550 on 8 pumps, or if it gets 614 with 7 pumps but only 567 with 8 pumps, you know it's time for some repairs.
    6. You can perform all those experiments you've been reading about. Do .22 pellets really develop 20 percent greater power than .177 in a given airgun? With a Talon SS and a spare barrel in the other caliber, you'll know for certain in a matter of minutes! Will Gamo Raptors really go supersonic in your Gamo CF-X? Is the Hunter 1250 Hurricane really a 1,600 f.p.s. air rifle with Raptors? With a chronograph, you'll know the answers to these and many more important questions.
    7. A chronograph tells you what those numbers on the Talon power adjustment wheel really mean! You will learn where to set the wheel for the best performance and perhaps save some air with every shot as you do.

    What do the numbers on the Talon power adjustment wheel and window mean? With a chronograph, you can find out!

    Are chronographs difficult to operate?
    Today's Chronys are easy to use. They come with complete instructions, and the video at the end of this article shows you just how quick and easy it is to set one up. Every time you shoot through the skyscreens, the number on the chronograph display changes to reflect the speed of that shot. It really couldn't be simpler.

    The moment you shoot, the Chrony display indicates the pellet's velocity. Here we see feet-per-second, but you can easily change that to meters-per-second. The cable is connected to the optional printer.

    What are skyscreens?
    The chronograph is a time-recording machine, and it needs something to start and stop the clock. Skyscreens do that. They are light sensors that are in line with each other in the red aluminum Chrony box. Both the start and stop skyscreen point up toward the sky - hence the name. When a pellet passes overhead, they sense a decrease in the light caused by the pellet's shadow, and that triggers them. Screen one starts the clock; screen two stops it. Because the clock is a crystal oscillator that vibrates at an extremely uniform rate, the number of oscillations that are collected between the start and stop screens represents the time it takes the pellet to travel that distance. Velocity is then calculated by the onboard computer, and the number is displayed on the LCD screen.

    Does it ALWAYS work?
    There is a region of sensitivity above the skyscreens that the pellet must pass through to trigger each screen. If it triggers one screen but not the other, you'll get an error message. The sensitive region has both height and width and varies in size with each caliber of pellet. A small pellet casts a smaller shadow, so the region of sensitivity is smaller.

    The instructions that come with the chronograph tell you that the area of sensitivity is roughly the shape and size of the trapezoid formed when the skyscreen diffusers are mounted. Actually, the real area varies with both lighting and pellet size, but it's always a little smaller than the area indicated by the wire stands and diffusers. On a bright day, strong sunlight can reflect off a shiny pellet and cause problems for the sensors. Always suspect light when your readings are difficult to get or they are nowhere close to where you expect them to be. Use the diffusers when the sun is bright or the clouds are moving about fast.

    The muzzle blast can trigger the start screen
    A jet of compressed air or CO2 can trigger the start screen under the right circumstances. The instructions that come with the chronograph explain this, so take the time to read and understand them. They recommend keeping the muzzle of a .22 rimfire 3 feet from the start screen, so you can get a little closer with an airgun. The type of powerplant and the power level of the gun you're testing will determine the actual amount of standoff you need.

    Using artificial light
    Artificial light can be used as long as it is constant. Regular incandescent house lights are fine, but lights that flicker, such as fluorescents, do not work. They trigger the skyscreens. A mix of fluorescents and incandescents is also bad; turn those fluorescents off! There has to be enough light for the skyscreen sensors to detect a shadow from the passing pellet. Positioning the skyscreens directly under the light and using the diffusers is often the best way to use the chronograph indoors.

    Other features
    The Alpha model I tested records several things besides velocity. There is the total number of shots per string (up to 32 shots with the Alpha model), the fastest shot and the slowest shot. It also calculates several statistics - average velocity, standard deviation and extreme spread. To access these data, you press the button labeled FU in the upper left corner of the faceplate and it steps you through the data. Additionally, these are international machines and will display velocities in either feet or meters per second. The instructions tell you how to make the change.

    If your shot doesn't register, there will usually be an error message telling you what's wrong. Error 1 means the first skyscreen didn't get a reading. Error 2 means skyscreen 2 didn't get a reading, and so on.

    When something goes wrong, the Chrony gives an error message like this. In this case, the second skyscreen did not "see" the pellet.

    Using the optional printer
    With the Chrony, you buy only what you need and nothing extra. However, one option most people will want is the ballistic Chrony printer. It provides much more than just a record of your shooting. For starters, it has a 16-foot cord, so it also serves as a remote control, so you can position the chronograph away from your shooting location and still control it. While the printer has no LCD display, you can read the velocity directly from the paper tape.

    The optional printer connects to both models. It runs on batteries or house current from the adapter provided. Besides recording everything that happens, the printer allows you to be 16 feet from the chronograph.

    This unit operates on four AA batteries but can also run on household AC current through the supplied adapter. That makes it a perfect accessory for the home experimenter.

    One nice thing about the printer is that it does the recording automatically. That leaves you free to shoot the gun. Another plus is the printer cable allows you 16 feet of separation from the Chrony, while still being able to see the velocities printed out as you shoot. Because the printer is an option, you can wait to buy it later. The chronograph works fine without it.

    Printer paper
    The printer comes with a small roll of paper contained inside its case, but you will want to use it with a standard printing calculator paper roll that comes from any office supply store. A wire axle pops out the top of the printer to hold a standard 2.25" standard printer paper roll. The printer ink roller is also a standard office supply item.

    Loading the paper is tricky at first, because the instructions are graphic only and not very clear. The secret is that the advance button only moves the paper one line at a time, so it takes a while to advance the paper through the printer. Once you know that, a new paper roll feeds easily.

    To sum it up
    A Shooting Chrony is a valuable addition to your shooting equipment. Once you start using one, there is no end of useful things you can find to do with it. The way the Chrony is made, you can start with a basic machine and add capability as you see fit. Next to the guns, themselves, this is one of the handiest things any shooter can own.

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