Energy Calculations - How Hard Does Your Airgun Shoot?
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. As a hunter, I want to know how hard my airgun is shooting so that I can be an ethical hunter.
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
In order to ascertain the power of your airgun, you will need to measure the velocity with a chronograph. 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.
If you enjoy math problems, work the equation another way to determine how fast your pellet is going. 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
For quick and dirty calculations, use the number 671 as a benchmark for figuring your FPE. You see, 671 fps is the velocity 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.
This sort of information is very useful when buying a used gun that someone has already chrono'ed, or has velocity figures in a log somewhere for an individual pellets performance is a certain gun. It helps you make an informed decision, and shows other airgunners that you are serious in your pursuit of air gun excellence!
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
In order to ascertain the power of your airgun, you will need to measure the velocity with a chronograph. 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.
If you enjoy math problems, work the equation another way to determine how fast your pellet is going. 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
For quick and dirty calculations, use the number 671 as a benchmark for figuring your FPE. You see, 671 fps is the velocity 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.
This sort of information is very useful when buying a used gun that someone has already chrono'ed, or has velocity figures in a log somewhere for an individual pellets performance is a certain gun. It helps you make an informed decision, and shows other airgunners that you are serious in your pursuit of air gun excellence!
posted by Randy Mitchell at
11:46 AM
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