by B.B. Pelletier
This report was suggested by reader G., but a lot of you have been talking about chronographs lately, so perhaps this is timely for everyone.
Don’t need no stinking chronograph
When I did the R1 Homebrew series of articles for The Airgun Letter, I needed a chronograph. And as far as I was concerned, that was the first time in my shooting life that I did need one. Up to that point, I considered chronographs to be silly toys that bored shooters used to add spice to their hobby. But when I was faced with the reality of comparing before and after tuning airguns in print, there had to be something more than just my word about how the gun was performing.
The R1 Homebrew articles are what grew into the R1 book that was published in 1995. While attending the Winston-Salem Airgun Expo in 1993, I bought a used F-1 Shooting Chrony for $45. That chrono lasted me about a quarter of the way into the book. I stopped using it when I got spurious velocity readings of 150 f.p.s. slower than should have been the case. The problem was twofold. First, the ancient chronograph I was using had cardboard windows that served as diffuser holders in front of both the start and stop screens. The windows were there to align projectiles over the skyscreens. Tens of thousands of shots had ripped the start screen window to the point that it overhung the start screen lens. I trimmed it back, but if I trimmed it any more the window would have been cut through and would no longer hold the white plastic diffuser, so I allowed some of the cardboard to overhang.
The other problem I had was the distorted shape of the hole through the windows forced me to shoot on a downward slant. That was when I discovered the problem with doing that.
At this point, the decision had already been made to write the R1 book, so Edith and I bit the bullet and bought an Oehler 35P printing chronograph–the gold standard of personal chronographs. That model is no longer available; but if you can use a Windows computer, the Oehler 43 is the same instrument with software to operate on your Windows computer. Several writers use a laptop with their 43, and the printer can be anything the computer hooks up to.
The 35 P was discontinued because the Oehlers were not able to obtain a supply of small printers to go into their chronographs. They are available, but not at wholesale prices in quantities small enough for the Oehler operation. I have more to say about printers later.
For years, I looked down on those who used Shooting Chrony brand chronographs, because the Oehler is such a superior instrument. It has a clock speed of 4 megahertz. At the time, I thought the Chronys were using a 100 kilohertz clock, but that may not be the case. The Oehler also has a second chronograph circuit in the system so you get two readings for every shot. One is a check against the other, and there are warning symbols if the difference is too great.
Then, I decided to write about chronographs. The Oehler 35P was no longer available and besides, does a hobbyist really need that kind of machine? So, I asked Pyramyd AIR to send me a Shooting Chrony Alpha chronograph and I reported on it in August 2005. The instrument I tested was quite an improvement over the old Chrony I had used more than a decade before. It set up easily and no longer had the cardboard windows that caused so much trouble. It probably also has a higher clock speed, though I cannot find any confirmation for that.
As I used the Chrony Alpha, I got used to how quick it was to set up. It sits on a table, making it ideal for my office, where the Oehler skyscreens are too high to align with the pellet trap. So convenience got me using the Chrony more and more. Now, I use the Oehler for articles and in the field, but the Chrony for everything else, which is more than 90 percent of my work.
Here’s the crucial thing. The Chrony doesn’t measure the velocity exactly. Neither does the Oehler. To measure exactly takes more accurate chronographs that are used by laboratories and by weapons testing stations. The skyscreens are separated by many feet distance and they are tailored for exactly what they’re testing.
But for the hobbyist, a Shooting Chrony gives a number that can be trusted. It will be accurate within 99.5 percent accuracy. Not more than one deviation in 200. When measuring something traveling 1,000 f.p.s., the error rate is about 5 f.p.s. That is certainly accurate enough for what we do.
Dr. Ken Oehler once told me that the biggest error in any chronograph was the accurate spacing of the skyscreens. They assume a certain separation which is fed into the formula for velocity calculation; and when that is off by as little as one-eighth inch, the readings are wrong. The Shooting Chrony has solved that problem by its design. When the box unfolds, the skyscreens are always separated by the correct amount. That’s a big plus, because other chronographs including the Oehler use a dimpled steel bar (conduit armor) to locate the screens.
Then, I did what almost all chronograph owners have done at least once. I shot too low and dented the chronograph case. I told Pyramyd AIR about the damage, and they told me to keep the chronograph. I did and have used it ever since. By the way, I also shot up my Oehler skyscreens. I did that while working at AirForce testing the Condor. Same screen got shot–the rear one.
What’s the answer?
So, which chronograph is right for you? Well, if you want to check pellet gun velocities, I recommend a Shooting Chrony Alpha, Beta or even the model F1. The more expensive models have memories and can calculate statistics. The cheaper models cost less.
Are other chronographs okay? Absolutely. Shooting Chrony is the best-known brand on the market, but the others work just as well. Shooting Chrony has a rebuild program if you shoot up your chronograph, and that’s a nice touch, plus I like the convenience of the box design. But any chronograph is better than no chronograph. Now that I’ve had one for a long time, I know more about why they’re good. I’ve shown you several examples recently in this blog, and I will continue to do so as we tune the FWB 124, for example.
What about printers?
Printers are less reliable than chronographs. The one on my Oehler has never malfunctioned, but the Shooting Chrony Ballistic Printer has. It sometimes fails to advance the paper, resulting in several readings printing on top of each other. Pyramyd AIR has recently experienced the same thing, so it happens but not on a regular basis.
If you buy a printer, be prepared to fiddle with it sometimes. It’s great for long strings of shots, but I generally don’t use it for short strings. Just make sure the paper advances after every shot.
Do you need a chronograph? Probably not, unless you know why you do. If all you like to do is shoot, you can forget a chronograph. But if you want to know the health of your airgun, a chronograph is a valuable piece of equipment to own.