We have all heard the old “1000fps” story from salesmen and new comer’s to airgun shooting, hell I was even suckered into it when I first started on my long road into airgunning. Its become a marketing gimmick used my airgun manufactures to keep up with the Jones'. Hatsan makes a 1000fps rifle so Gamo must as well, Hatsan responds with a 1200fps rifle and the cycle continues.
But what exactly does it mean, is it important and can we even believe what’s written on the box?
Ill start with the latter as it’s the start of that dark road of ignorance. Can we believe what’s written on the box or what the salesman is telling us? Unfortunately you cannot! Advertised muzzle velocity is at best a product of very specific circumstances and at worst a ball faced lie. Manufacturers use super lightweight pellets and shoot at the lowest possible altitude to achieve these results, not exactly a true reflection of how the rifle will perform under normal operating conditions. If you want that information then you need to shoot the rifle over a chronograph.
So what is muzzle velocity and is it really important? Well velocity is speed. Nothing more or less than how fast the projectile is moving. This is important as far as trajectory is concerned and for high level competitive shooters matching velocity to a specific barrels twist rate and harmonics. Not really the concern of the average shooter.
So why do people seem to care so much about how fast the pellet is moving? The answer is that people often confuse speed and power. More speed must equal more power, it makes sense does it not? Well no, not really when you start to think about projectile weight. A heavy thing travelling at a certain speed will have more energy than a light thing going at the same speed. Energy of a moving object is a product of its speed and its weight. Neither value gives any useful information without the other.
The analogy iv come to use most often when explaining the difference is the “.45 vs 4.5” comparison. Lets take a .45ACP round and shoot it over a chronograph, an average load will give around 850fps, nowhere close to 1000fps airguns but obviously far more powerful. But why? A .45 is a firearm round yet its still slower than an airgun? Well a .45 bullet weighs 230grains (about 15grams) while a 4.5mm pellets comes in at around 8grains or half a gram. Personally if I had to make the choice id rather be shot by a 4.5 than a .45.
SPEED MEANS ABSOLUTELY NOTHING IF YOU DON’T KNOW THE WEIGHT OF THE PROJECTILE!!!!
Lets break it down in terms of airgun shooting, most “1000fps” rifles have a muzzle energy of about 12fpe (foot pounds of energy) or 16j (Joules) if you’re like me and detest all things imperial. Below is a chart of muzzle velocity from just such a gun (this is a test of the maths not of an actual gun) The only variable is the weight of the Pellet.
From that is easy to see how a pellets weight effects the muzzle velocity. With the same gun we got from 600fps all the way to 1200fps and all we did was change the weight of the pellet, The muzzle energy has remained constant at 16j. So the salesman didn't really lie to you when he sold you that 1000fps airgun, he simply neglected to tell you what was travelling at 1000fps. In this example it’s a 5gr pellet however the average lead pellet weighs about 8gr so your 1000fps gun is really an 800fps gun.
So the next time you hear someone bragging about the speed of their gun the only correct response is “oh yeah? With what weight pellet?”