by B.B. Pelletier
This is a reprint of an article I wrote for Airgun Revue #3, which was published in 1998.
The airgunner of yesteryear was a happier person than his modern counterpart. If he wanted to see how accurate his gun was, he shot at something. If he hit it, he looked for a smaller target to shoot until the parameters of accuracy were firmly established. If the gun had to be held right or left, high or low, or some combination of these, he was willing to do it because that was the way the gun shot. Period!
It worked the same way for velocity. If the projectile made it to the target and did whatever was expected of it, velocity was adequate. Punching holes in paper is easier than downing large game animals, and our simple countryman with his primitive airgun was smart enough to know that. He lived at a time we now call B.C.–before chronographs.
Unfortunately, for those of us on the cusp of the third millennium [of course, we’re in it now], writers of earlier times were also hamstrung by the lack of instrumentation. Their descriptions of velocity, power and accuracy sounded like political speeches, filled with subjective words like “substantial,” remarkable” and “amazing.” All of which gave rise to a body of half-truths and downright prevarications regarding the power of ancient big bore airguns.
Today, an airgun maker has to build his big bore pieces to compete against the airguns of history, which reportedly threw huge lead balls at 900 f.p.s. with sufficient accuracy to kill a man 100 yards distant. It would be nice to fire these oldies once again so the claims could be verified, but of course they’re both too valuable and too embrittled by age to permit that. So, they repose at permanent rest, shielded by their value while the myths about them continue to grow.
New info about old guns
Except for one thing–airgun maker Gary Barnes has conducted tests showing that round lead balls deform along rigid lines until the ball is completely fragmented by the force of impact. Here’s the big news: this phenomenon happens irrespective of caliber! His claim is that all lead balls deform in more or less the same fashion when they impact a rigid steel plate at a given velocity. A .350 caliber ball impacting a steel plate at 350 f.p.s. will look the same as a .535 caliber ball going the same speed, except for the difference in size. Thus is born the science of “splatology,” or the study of lead “splats” to determine the impact velocity of the ball that created them.
Barnes noticed this relationship very early in the testing of his first big bore guns. The phenomenon was so intriguing to him that he made up “splat boards” containing a spectrum of lead balls that had impacted at different velocities. These he mounted in series, ranging from lowest velocity to highest. The velocities were obtained from an Oehler model 35 chronograph placed in front of the splash plate. He then carved the velocity for each ball into the wood next to the recovered splat. All his splats were produced by a one-inch steel splash plate that stands perpendicular to the flight of the ball, so it’s identical to the plates mentioned in the early airgun documentation.
It doesn’t matter when it was shot; a splat tells the same story forever! It’s important to keep in mind the fact that the splats reveal only the velocity upon impact. If the actual muzzle velocity is desired, additional calculation is required. That depends on how far the muzzle was from the impact point. Fortunately, this distance is sometimes given in literature. It’s possible to calculate velocity for tests conducted a century ago, providing the splat is accurately represented (usually by a drawing, but in this century photos were also used) and the distance to the plate is given.
The “splash plate,” as it’s called, must be rigid for the results to be consistent. If not, some of the ball’s energy will be used to move the plate, which results in a splat that looks like it’s going slower. We know the ancients were aware of this phenomenon because it’s mentioned in their notes. In W.H.B. Smith’s book, The Standard Encyclopedia of Gas, Air and Spring Guns of the World, the author mentions that European makers were still testing the power of their modern pellet rifles in 1956 by firing them against steel splash plates.
How to calculate velocity without a chronograph
Older English writings state that big bore airgun velocities were gauged by flattening the ball against a steel plate at a specified distance. In the book Air Guns and Air Pistols by L. Wesley, there’s a photograph of flattened balls shot from an air cane, representing the progressive lowering of velocity as the pressure dropped. It’s obvious to anyone who sees the photo that lower velocity results in a ball that is less flattened.
With this technique, it’s possible to examine the older writings about big bore airguns and determine the impact velocity from drawings of recovered balls. Since the steel or iron plate test was a common one when these guns were new, there are several drawings of flattened balls that accompany the guns. Caliber doesn’t matter, remember, since all balls exhibit the same characteristics when they impact a metal plate at the same speed. Here’s an abbreviated version of Barnes’ observations:
At or below 250 f.p.s., the ball will be smashed perfectly flat on the impact side, with the opposite side still round. It will look like a perfect hemisphere, with little of the ball spreading out from the edges of the hemisphere.
At 275 f.p.s., the edge of the ball starts fanning out from the central hemisphere. Barnes calls this “feathering.”
Above 300 f.p.s., the hemisphere that was intact starts to thin out. It’s no longer a true hemisphere.
At 350 f.p.s., the remainder of the ball begins to look like it’s “melting” toward the sides, which are now starting to show signs of separating into both large and small “petals”.
At 400 f.p.s., the ball is nearly flat and separated into distinct petals. Little remains of the original hemisphere.
At 450-480 f.p.s., the ball is completely flat, and the petals are tearing deeper toward the center of the ball.
At 550 f.p.s., the petals are well-formed and very deeply separated. After this point, they start to break off.
At 600 f.p.s., the ball has lost two-thirds of its petals. Now, the center of the ball starts to look like the whole ball did at 450 f.p.s.
At 609-610 f.p.s., a strange thing happens. The center of the ball recoils off the splash plate, and the petals that remain attached to the center recoil back toward the steel plate.
At 650 f.p.s., only the center of the ball remains. Sometimes, it looks like a smaller whole ball, but often there are angular sides and irregular shapes, where major petals were joined. The surface that struck the steel plate is now pointed in the center.
At 675 f.p.s., the center of the ball is smaller. It’s starting to disintegrate into flakes.
Above 700 f.p.s., the center is destroyed; only flakes remain. You can taste vaporized metal in the vicinity of the splash plate.
Test your new splatology skills!
Try your hand at guessing the velocity of the following splats. The featured splats went through the chronograph at recorded speeds. See if you can guess their velocity by comparing them to the splat boards! I’ll publish the actual velocities in tomorrow’s blog.