November 7, 2020

How To Measure The Power Of An Air Rifle

Many times, when we look for an air gun to buy, we look for its power. It’s always very exciting to own a powerful air gun. Many times there are many misconceptions about the power of an air gun. Even many expert shooters fail to tell the power of an air gun. Sometimes there are mischievous sellers sell air guns by overstating its power. Moreover, as per the Indian Arms Act, 1959 (Amendment 2016) it is illegal to own an air gun beyond .177 Cal. And 20 Joules power without a proper license. So, it is always good to know the power of your air gun. Now, you can see the caliber of your air gun engraved on its barrel or stock, But the power is not written anywhere. So it is up to you to determine it.

The power of an air gun is known by its muzzle energy; the measuring unit is Joules. Muzzle energy is simply the kinetic energy of a projectile measured at the moment it exits the muzzle of a gun, which is when it is going fastest. The general formula for the kinetic energy is:

    \[ E_k = \frac{1}{2}mv^2 \]

where

v is the velocity of the bullet

m is the mass of the bullet.

Although both mass and velocity contribute to the muzzle energy, the muzzle energy is proportional to the mass while proportional to the square of the velocity. The velocity of the bullet is a more important determinant of muzzle energy. For a constant velocity, if the mass is doubled, the energy is doubled; however, for a constant mass, if the velocity is doubled, the muzzle energy increases four times. The standard unit of above E_k will be in unit joule if the mass, m, is in kilogram, and the speed, v, is in meter per second. In imperial system, E_k will be in unit foot-pound, m will be in gram and v will be in feet per second.

To measure your air gun’s power, here are the things you need.

Once you’re equipped with the above-mentioned instruments, you are ready to run your experiment. Make sure you use branded high-quality pellets, not the locally made ones. High-quality pellets provide the most optimum consistency. We recommend using RWS, JSB, Gamo air pellets, though you are free to choose your own pellets.

Step 1

Note down the grain of the pellets which are to be used for the experiment.

Step 2

Measure the muzzle velocity of your air gun using the ballistic chronograph with each pellet. Note down the readings and calculate the average value. Please note that the muzzle velocity may not be exactly the same due to several factors, which is why we need an average value. In case, if you don’t know how to do it, you can read our article about How To Measure Muzzle Velocity of A Gun.

Now, when you have the values, use our muzzle energy calculator below to determine the power of your air gun.

Muzzle Velocity: FPS

Pellet Weight: grain

Power is:

0

joules

Want To Know How It Works?

This section of the article is for curious ones. If you are still reading this article, we assume you want to know the sheer mathematics behind the calculation method.

Multiply the weight of the pellet (in grains) times the square of the velocity and divide that number by 450436.7. That last number is a constant created by multiplying two times the acceleration of gravity by 7,000 – the number of grains in a pound. At different points on Earth’s surface, the free-fall acceleration ranges from 9.764 m/s2 to 9.834 m/s2 depending on altitude and latitude, with a conventional standard value of exactly 9.80665 m/s2 (approximately 32.17405 ft/s2). This does not take into account other effects, such as buoyancy or drag.

You will get the result of the above-mentioned calculation in ft-lbs. Now, to measure it in Joules, multiply the result with 1.35581795. The mathematical formula is as below:

    \[ \left\{ E_k \times \left( \frac{1}{7000 \times g} \right) \right\} \times 1.35581795 = J \]

    \[ \therefore \left\{ \frac{mv^2}{2} \times \left( \frac{1}{7000 \times g} \right) \right\} \times 1.35581795 = J \]

    \[ \therefore \frac{mv^2}{7000(g \times 2)} \times 1.35581795 = J \]

where

m = Mass

v = Velocity

g = Gravitational acceleration

E_k = Power in ft-lbs

J = Power in joules

Now you know the math. We did an experiment with Precihole NX200 Athena.

Measuring Power of Precihole NX200 Athena

We measured the power of Precihole NX200 Athena using the above mentioned mathematical formula under the given circumstances:

Air Rifle: Precihole NX200 Athena .177 Cal Break Barrel Air Rifle

Air Pellet: RWS R10 Match Rifle 4.50 mm 8.2 grain

Measurement Unit: FPS

Shot Count: 5 shots

Result: 849.1, 840, 852.1, 834.1, 817

Average Velocity: 838.46

Muzzle Energy: 17.35 Joules

Why you should measure the power of your air gun

Should you really care about it? We believe you should. Sports shooters may need to tune the power of their air guns to achieve the best possible score. Generally, there are several reasons. If you monitor your air gun’s power performance on a regular basis, it’ll be easy for your maintenance. As per the Indian Arms Act 1959 (Amendment 2016), possessing an air gun/firearm beyond 20 Joules is prohibited without a proper license. So, if you are thinking to buy any imported air rifle with a muzzle velocity of 1100 or 1200 FPS, then you need to calculate the power and think again. Sometimes a deceptive seller may sell an underpowered air gun to you overstating its power if you are not careful.

There can be several more reasons we may miss here but now you know how to measure the power of your air gun. Have you checked your air gun’s power lately? Share with us your results in the comment box.

 

6 thoughts on “How To Measure The Power Of An Air Rifle

  1. Very well explained article. The “Calculator” will surely help everyone to check the muzzle energy of his/her existing Air Gun or before buying a new Air Gun to stay within the permissible legal limit of the country.

  2. I was looking through some of your articles on this internet site and I conceive this website is real instructive! Keep putting up.

  3. There is certainly a great deal to find out about this issue. I like all the points you made.

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