AOA Blog

Just the other day, I got an email from one of my main contacts at www.airgunsofarizona.com – the good folks who graciously support this blog.

My contact was complaining, ever so gently, that they tend to get certain questions again and again. They are, in no particular order:

• “I see you rate the airgun in ft/lbs (foot-pounds), but how many FEET PER SECOND does it shoot?”
• “Why don’t you rate in feet per second?”
• “Why is your feet per second rating lower than the manufacturer’s?”

I told my contact that I would attempt to answer these questions in a way that they might not come up so often in the future. So here goes.

“I see you rate the airgun in ft/lbs (foot-pounds), but how many FEET PER SECOND does it shoot?”

To really get a handle on this question, we have to go back in time a little. Over the past dozen plus years that I have been writing about airguns, I have noticed a creeping trend among airgun manufacturers, particularly those that sell their products in the big-box discount stores. That trend, quite simply, has been to advertise the speed of the airgun prominently on the box, and a kind of arms race has developed. If one manufacturer says “1,000 feet per second,” the next manufacturer will crow “1,200 feet per second,” and pretty soon a manufacturer will brag “1,500 feet per second!” The manufacturers do this, I presume, because the poor consumer, who knows relatively little about airguns, will naturally assume that a faster airgun is better than a comparable airgun that is slower.

But this kind of airgun advertising really does the consumer a disservice. To discover why, we have to start with a few key physical facts. Key fact number one: the sound barrier at sea level is right around 1,100 feet per second. This is important because, as the speed of a pellet approaches the sound barrier, it enters a region of turbulence that seriously interferes with shooting accurately. This is also true of a pellet that is initially shot at high speed and then drops very quickly below the speed of sound. It is far better to shoot slower and more accurately than to shoot a pellet at higher speed and miss. For this very reason, most of the country’s field target shooters set up their guns to shoot no faster than 950 feet per second, and many shoot much slower.

(And – as an aside – it is possible to do very accurate shooting with relatively low-speed airguns. Just ask the air pistol silhouette shooters who use the Daisy Avanti 747. Olympic 10-meter competitors shoot rifles that send the pellets down range at around 600 fps.)

Key fact number two: there are no – repeat NO – airgun powerplants that launch pellets fast enough to keep them above the speed of sound for any appreciable distance. In the field of powder-burning varmint rifles, you will find cartridges that will launch bullets at 3,000, even 4,000 feet per second. The varminter is relying on the bullet staying at supersonic velocity all the way to the target to maintain accuracy. But this simply isn’t possible with an airgun powerplant.

Now, I can almost guess what you are thinking: “But what about those airguns that advertise 1,500 feet per second?” Okay, I’ll tell you. First, they achieve those velocities by shooting very light pellets that do not retain their velocity well over distance. Second, they do not obtain excellent accuracy using those very light pellets. A few years ago, I tested a spring-piston air rifle that was promoted as generating 1,500 fps. With very light non-lead alloy pellets, it would, indeed, achieve velocities in the mid-1400s, but at 50 yards, it delivered five-shot groups that were about six inches in diameter. When I fed that same rifle heavy pellets and slowed the velocity down to around 930 fps, the group size shrank to less than 1.5 inches at 50 yards. Slower was much more accurate.

So when you ask “How fast does it shoot?” You are basically asking the wrong question.  Let’s do a little thought experiment for a moment. Let’s pretend that you are napping on the couch on a Sunday afternoon. Now, here comes Uncle Jock, sneaking up on you, with a sphere in each hand. My plan is to drop one of these spheres on your head from a distance of six inches. Since gravity is a constant, either sphere will drop on your sleeping cranium at exactly the same speed. Now, here’s the question: one of the sphere’s is a table tennis ball which weighs only a fraction of an ounce, and the other sphere is a bowling ball, which weighs several pounds – which one would you prefer that I let slip from my fingers? Unless you are incredibly weird in some way, I’m pretty sure that you would prefer the table tennis ball because, even though it would be falling at the same speed as the bowling ball, it is lighter and will hit with less force. The bottom line is that the weight of the projectile matters as much as the velocity. In the world of airguns, the force of a pellet is measured in foot-pounds of energy.

So, if you ask “How many foot-pounds of energy does it generate at the muzzle, you are getting a much better idea of what the relative power of the airgun is. That also explains why www.airgunsofarizona.com does not generally rate airguns in feet per second.

If you want to calculate foot-pounds of energy for yourself, here’s how you do it: take the velocity of the pellet in feet per second and square it (multiply it by itself). Take the resulting number and multiply that by the weight of the pellet in grains. Finally, divide that number by 450240. So, if your airgun is shooting 7.9 grain pellets at 800 fps, here’s the calculation: 800 x 800 = 640,000. 640,000 x 7.9 = 5,056,000. 5,056,000 divided by 450240 = 11.2295 foot-pounds of energy.

Why is your feet per second rating lower than the manufacturer’s?”

This is a lot easier to answer: most manufacturers use really light pellets to achieve their velocity ratings. Super light pellets, however, are not generally what most people shoot with. The criteria that airgunners should use in selecting the right pellet for their air rifle or air pistol is not which pellet shoots the fastest, but which pellet delivers the best accuracy.

Til next time, aim true and shoot straight.

–          Jock Elliott