Have you ever wondered if your new airgun actually reaches the “up to” velocities stated in the marketing? I remember when I bought my second airgun. It was a Beeman GH150 22 caliber that promised up to 800 FPS. I was unbelievably excited to get in this new gun and experience “real” power.
As I began to read more and more information online, I realized that many manufacturers tend to exaggerate when it comes to their “up to” velocities. I wanted to know exactly what my airguns were shooting. The only way to do this was to purchase a chronograph. Now you can get a basic chronograph for around a hundred dollars, but there are some more advanced models such as the PACT Professional-XP chronograph that have a ton of really cool features that cost much more. As you can imagine that I started with one of the hundred dollar options.
I was amazed to find that my 800 FPS airgun was actually shooting in the midst 600s. Regardless of what pellet I tried I never got close to that 800 FPS mark. But chronographs can do so much more than just tell you if your rifle the shooting up to the manufacturers marketing statements, and that’s what I’m going to talk about today.
A chronograph works by measuring the time it takes from a projectile to travel a certain distance. There are at least two sensors on a chronograph. These sensors “see” the projectile and measure the time it takes to travel between them. The computer in the chronograph then displays a value, normally in feet per second.
So what are some of the advantages that a chronograph can bring to the average airgunner? Most importantly, it can provide valuable diagnostic information. Many times I’ve spoken with airgunners about an airgun that has all of a sudden stopped shooting accurately. Short of dismantling the airgun in question, a chronograph can provide insight regarding what may be the problem. Most of the time it’s an issue with one of the seals or the power plant (i.e. spring or gas ram) and a chronograph can very quickly identify this.
Years ago I had a Remington NPSS rifle. It was one of my favorite airguns and I was very pleased with its accuracy and power. One day, while showing a buddy of mine my collection, I picked up the NPSS and fired it down range. What was once a very accurate shooting airgun had become horribly inaccurate and seemed anemic. Because I had a baseline of how this gun shot in its prime, I set up my chronograph to test its current performance. Immediately I knew that the gas ram had a problem because it was once shooting over 700 FPS but was now shooting only an average of 350 FPS with an extreme spread of about 100 FPS. With that diagnostic data in hand I was able to arrange a simple warranty replacement with Crossman who took care of the problem without question.
So beyond providing basic diagnostic data, what can a chronograph do for the average airgunner? As you shoot multiple shots, these are called shot strings, most chronographs will calculate other important information such as; extreme spread, standard deviation, and average velocity. Each of these values is an important measure of how well your airgun is performing. The simplest of these values is the average velocity.
The average velocity is the average feet per second across all of the shots in your shot string. I use the average velocity as a key component when I calculate basic trajectory. All you need is the ballistic coefficient of your pellet (most of the time easily found on-line), the average velocity of your airgun, and a software package like Hawke’s ChairGunPro (now available for PC, MAC, iPhone, & Android). There are some other variables that you may need but the essentials are your average velocity and the ballistic coefficient of the pellet you’re shooting.
When I talk about the extreme spread in a shot string, it relates to the difference between your fastest and slowest shots in the string. Ideally you want a very low extreme spread. This means that your airgun is very consistent, and there is not a large change in velocity from shot to shot. This is very important if you want to see consistent accuracy.
The final value that I’ll discuss today is standard deviation. Without getting into a lot of mathematical mumbo-jumbo, standard deviation looks at the average velocity and examines how each shot varies from that average. A low standard deviation means that you have a very consistent shooting airgun. Conversely, a high standard deviation means that your airgun is not shooting consistently. This can affect your point of impact from shot to shot.
Some chronographs go much further. For example when hunting for a new chronograph I settled on the PACT Professional-XP chronograph. Not only does it provide all the standard information but also has a built in ballistics calculator that can determine ballistic coefficient as well as calculate trajectory and impact energy. It also has a built-in printer, and a PC interface. The model that I purchased came equipped with infrared sensors that allow me to shoot indoors without any problems or interference from florescent lighting. (Most chronographs must be shot outdoors to provide adequate light for the sensors. Some chronograph manufacturers provide optional lighting kits.) I’ve owned several chronographs over the years, but the PACT Professional-XP chronograph is certainly my favorite to date.
So if you’re new to airgunning and you want to really “know” how your airgun is performing, then the first piece of equipment you need to add to your collection is a good chronograph. Airgun depot has many chronographs on their site with various features and functions. For more information please feel free to call 1-866-477-4867 for more information or email us and one of our customer service reps will be more than happy to help.
