Velocity vs. accuracy: Does it REALLY matter? Part 1
by B.B. Pelletier
My apologies to Jane Hansen. I’d promised her another report on the Blizzard S10 today, but I came down with a horrible stomach flu Sunday morning. My wife, Edith, quickly pulled together this article from the April 2001 issue of the Airgun Letter, as I was in no shape to give the S10 a fair shake.
On to day’s blog.
We say pellets can’t travel much over 900 f.p.s. and still be accurate, but does anyone really know for sure? If 1,200 f.p.s. is too fast for accuracy, why would pellet gun manufacturers tout that speed and greater for their magnum air rifles?
These days, many manufacturers offer at least one air rifle with a top velocity well over 1,000 f.p.s. It’s easy to speculate that they’re just doing it because the public doesn’t know better. But is that really the case? Or, is supersonic velocity not the horrible block to accuracy it’s cracked up to be?
Can an airgun be accurate at 100 yards?
I plan to shoot an airgun at 100 yards for the long-range accuracy test. That seems to me to be the equivalent of shooting a 45/70 at 500 yards or a 30/338 at 1,000. When I shoot that far, I want all the velocity possible consistent with accuracy. Yet, the diabolo pellet I will shoot is a high-drag projectile that starts putting on the brakes the moment it exits the muzzle.
All projectiles slow down, of course, but the diabolo is designed to do it very well. It’s the antithesis of the Sierra Matchking 168-grain boattail, which is designed to slip through the air with a minimum of resistance. Think of the Sierra as a spear and the diabolo as a badminton birdie.
Why do I want all this speed? Simple–to flatten the trajectory. A diabolo pellet leaving the muzzle at 900 f.p.s. will drop 3-5″ by the time it reaches 50 yards, depending on the pellet used. You compensate for this drop by aligning the sights so the pellet appears to rise for a while before falling again, but that adds another twist to the equation. You can be just as far off-target at 10 yards as you are at 50 if your sights are positioned to give apparent rise for the first 30 yards of flight! How much better it would be if you could just sight-in at 50 yards and know the pellet would always be within an inch of the line of sight from the muzzle out to 70 yards.
Higher velocity will help flatten the trajectory, even though the diabolo shape of the pellet still slows it down rapidly. So, why don’t more airgunners shoot at speeds above 1,000 f.p.s.? Because of the sound barrier.
Chuck Yeager wasn’t the first to break the sound barrier
When I was a boy in the 1950s, the sound barrier was on everyone’s lips–especially little boys! Chuck Yeager had officially broken through it in level flight for the first time in 1947, paving the way for a new age of high-speed flight. By the time I became aware of things, people were already talking about Mach 2 and Mach 3, as new records were being set all the time.
What is the sound barrier? Webster’s Encyclopedic Unabridged Dictionary defines it as “a sudden large increase in aerodynamic drag that occurs as the speed of an aircraft approaches the speed of sound.” Of course, the object doesn’t have to be an airplane for the effect to occur. It happens to all objects, including pellets.
I remember the early movies about breaking the sound barrier. They emphasized the extreme buffeting an airplane suffered as it approached the speed of sound. Indeed, many early attempts on the sound barrier ended when the airplane actually broke from the stress. But mankind had already been exceeding the sound barrier for more than two centuries by the time Yeager made his historic flight. They had done it with bullets.
If you’re a shooter, you should be interested in aerodynamics
By the time gunpowder had advanced to the stage where it was reliable and relatively clean burning, musket balls were breaking the sound barrier. They were also getting buffeted, just as Captain Yeager would in his Bell X-1, only there was no way anyone could sense it. By the 1730s, men like Daniel Boone knew that a rifle that cracked was shooting better than one that sounded off with a hollow boom. They didn’t know what made the crack, just that it was the right way for a rifle to sound. They shot round lead balls in their rifles–balls that also slowed down rapidly, though not as fast as diabolo pellets do. But because their rifle balls were made of solid lead, the aerodynamic buffeting did very little to alter their path to the target.
Later, men learned to spin projectiles faster with a tighter twist rate, allowing the use of longer bullets. These bullets were even less affected by the buffeting because they weighed two to five times as much as the round balls. Because they were so heavy, they were not as affected by drag as the smaller balls, hence they retained more of their initial velocity for a longer period, which also meant they went farther at supersonic speeds. That was what was needed to extend rifle accuracy from 100 yards to 1,000 yards and even beyond. By the 1870s, long-range rifle marksmanship was as popular as professional football is today.
During this surge of rifle marksmanship, but in no way connected to it, the small-caliber airgun was born. In 1842, the Oscar Will company made a dart-shooting airgun. By 1876, Quackenbush started cranking out relatively inexpensive pellet-shooting guns by the hundreds. In 1886, the Markham company came out with the very first BB gun, which was soon followed by the first model from Daisy. And the rest, as they say, is history.
Airguns proliferated in greater numbers than ever before as their prices dropped steadily. By the 1920s, larger-caliber airguns, the ones we now call “big bores,” were but a memory and the ubiquitous BB gun was dominating the market–at least in the U.S. Elsewhere, precision air rifles and pistols began to rise from the ashes of World Wars I and II. They were beautifully made and shot as well as the technology of the time permitted, but they were all relatively low-powered by the standards of today.
It wasn’t until 1982, with the introduction of the Beeman R1 Supermagnum air rifle, that a production airgun intentionally shot faster than 1,000 f.p.s. That marked the first time the high-drag diabolo pellet was pushed anywhere near the aerodynamically challenging sound barrier. In four centuries of airguns, there have been less than 20 years during which pellets have been pushed past (maybe) their design limits.
The Beeman R1 was the first production air rifle that could reliably exceed 1,000 f.p.s. It started a trend toward higher velocities that took diabolo pellets where they had never gone before.
The R1 was soon upstaged by the even faster Laser option for the same rifle. That was followed by the expensive Venom Mach I rifle (interesting name, no?) and then a bit later by the much more affordable RWS model 48/52–an air rifle that has no problem pushing .177 pellets out the spout at 1,100 f.p.s. After about 1986, the number of guns that could exceed the sound barrier grew steadily with each passing year.
But the diabolo pellet hasn’t changed much since it was first invented almost a century ago. Its high-drag, forward-weighted shape was purposely created to keep the nose of the pellet pointed along the flight path when shot from a smoothbore airgun. Like a dart or arrow, the drag on the tail automatically orients the pellet in flight, making spin unnecessary–a good thing when you’re shooting an airgun like a Gem smoothbore. But not so good when you want to shoot past the sonic barrier.
The diabolo pellet is shaped like a child’s top. The narrow waist, flared skirt and hollow base all increase the amount of drag on the projectile. That, plus the forward-biased weight distribution, keeps the pellet stabilized in flight–with or without a spin.
I often try to find parallels to airguns in other shooting sports. Where the question of accuracy versus velocity is concerned, I don’t have to look any farther than the good old .22 rimfire. As everyone knows, slower is more accurate with the .22 long rifle. Unless all the competitors, ammunition manufacturers and gun makers are wrong, the most accurate .22 rimfire shoots a bullet at something well under the sound barrier. Eley Tenex, Federal Gold, Lapua Match and the other top names in match-grade rimfire ammo all stay well under 1,100 f.p.s. These are the cartridges folks are shelling out $10 and more for just 50. You and I try to buy a “brick” of 10 times that amount for the same price, but we don’t compete with the same crowd, do we? [Obviously, ammo prices have changed a lot in the 8 years since this article was written!] We like to bounce tin cans around, while they’re competing for gold medals on the world stage.
The weight of the majority is going with subsonic rimfire ammunition where top accuracy is concerned, and they’re voting with their deep pockets. These shooters typically buy 10,000 rounds at a pop at those high prices. When was the last time you bought 10,000 pellets, for a fraction of the cost, and didn’t flinch?
Remember, too, rimfires shoot heavy lead bullets–not thin hollow cylinders. Though some of those bullets have cupped bases and “heels,” they don’t have nearly the drag of our diabolos.
Stay tuned for part 2 later this week.