Calculating the Power of Your Airgun
When it comes to airguns, many people regard the airgun as a toy. However, as I and many others can attest, the airgun is a very viable tool for hunting and pest control. And one of the things that concerns a hunter the most is the power available from their airgun.
There is a simple mathematical equation that you can use to determine the power that your airgun develops. Here is the equation:
Mass (in grains) X velocity (in feet-per-second) squared, divided by 450240 (gravitational constant).
Now what does that mean? Simply put, you multiply the speed of your projectile by itself, then multiply that answer by the weight of your projectile. Then divide by 450240, and you have your fpe (foot pounds energy). Here’s a test for you:
What is the fpe of a 14.3 gr Crosman Premier pellet going 800 fps?
Answer: 20.32 fpe
You really need a chronograph in order to determine the accurate speed of your pellet. Many airguns are tested with the lightest ammo available, and the advertising will state the speed as an impressive marketing tool. However, with some reason on your part, you can get a more accurate idea of how powerful your airgun really is, and then determine if it is suitable for the purpose you have in mind.
Now lets assume you know the energy of your projectile at the muzzle, and you want to know how fast that little pellet is really going. Here’s the equation for figuring out the answer:
Take the foot pounds energy (fpe) of the gun, and multiply it by the 450240 we used above. Then divide that answer by the weight of your projectile. Then calculate the square root of that answer (I just hit the square root button on my calculator!), and you have your answer.
To test yourself, figure the fps of an 8 gr. pellet that yields 8 fpe at the muzzle.
Answer: 671 fps
Here’s another little gem that helps you with quick calculations. There is a magic number of 671 that assists the shooter with figuring fpe. If you have a projectile that is going 671 fps, then the fpe that projectile develops at the muzzle is the weight of the projectile. So, if you are shooting a 14.5 gr RWS Superdome from a .22 air rifle, and the chronograph tells you it is going 671 fps, then you know the fpe is the weight of the pellet….14.5.
Just a few things to help you enjoy your airgunning a little more each day.
