How powerful were the big bore airguns of the past?: Part 1
by Tom Gaylord
Writing as B.B. Pelletier
This report covers:
- New blog section — History of airguns!
- How powerful?
- Wood was first
- Iron and steel
- How fast — Spaltology
- Velocity of the big bore airguns of antiquity
- Available air pressure
- Why this is important
New blog section — History of airguns!
Today I announce a new section of the blog that will be dedicated to the history of airguns. Monday’s posting about the Rise of the BB gun was the inaugural report for the series — History of airguns. Today is the second in what Pyramyd Air and I hope will become a favorite of blog readers.
My goal is to document the history of airguns in these reports, and the really neat thing is, we will keep track of all these reports on a special page that holds the table of contents. The articles listed will be links, so all you need to do is hover your cursor and click to get there!
As the number of reports grows, they will be grouped into categories for ease of management. For example, all BB gun reports will be in the BB gun section, and so on. But, until we get a few more reports, the links will just be listed as they come.
Today’s report addresses the power of the big bore airguns of the past. How powerful were they and how did people living 300 years ago measure the power of an airgun? They didn’t use chronographs; those were still hundreds of years in the future. So how did people in the year 1715 gauge the power of an airgun — or for that matter, of a firearm? They started simply. They judged the force of a shot by what it could do, and they set up tests to demonstrate those results.
Wood was first
The first “test” was to see how deeply a ball fired from an airgun penetrated into a piece of wood. That’s not so different from today — is it? But wood has many problems. Should it be a living tree or wood that has been cut into lumber? If lumber, should it be green or dry? Does it matter if the shot goes across the grain or with it? Does the species of wood make any difference? And so on. As it turns out, soft woods like balsa provide vastly different results than hard woods like ironwood and hickory. And it is easier to penetrate across the grain, rather than traveling with it. Wood is not a very good way to test the power of a gun.
Iron and steel
What about iron and steel? While there are many alloys of both metals, the outcome of shooting a lead ball at them isn’t affected by those differences as much as it is with wood. This was widely accepted in the past, and testing of airgun power was tied to how deformed a ball would be after it hit a steel plate. But before we continue, you must understand that the plate the ball strikes has to be immobile for what follows to make sense. If the plate can move, some of the ball’s energy is used to move it, thus rendering the flattened ball less accurate for what comes next.
In the 1957 book, Smith’s Standard Encyclopedia of Gas, Air and Spring Guns of the World, by noted gun writer W.H.B. Smith, there is a drawing of a smashed lead ball from history. It was fired from a Perkins steam gun (ca. 1825) at an immobile iron plate 100 feet from the muzzle. The ball is shown in its original shape and also as it flattened against the iron plate. If the image in the book is life-sized, the ball measures 0.453-inches in diameter. That sounds about right for a gun of the period, though it is on the small side.
Ball from Perkins gun, before and after striking an iron plate at 100 feet. Image taken from Lateral Science, a scientific pamphlet published July 8, 1912. Image B is on the left and C is on the right.
I know that steam is not air, but the principal of this gun remains the same. The Perkins gun had a barrel length of 6 feet and was capable of firing 500 to 1000 balls per minute. Yes, it was fully automatic — not in the sense that a machine gun is automatic, but just as a water hose sprays water in a continuous stream, so the Perkins gun sprayed bullets. Perkins’ gun generated the unbelievable steam pressure of 900+ psi, at a time when air pressure was not able to compete. More on that in a moment.
How fast — Splatology
Before I talk about the air pressure the antique airguns generated, let’s first look at that deformed ball — for it actually tells us how fast it was traveling when it hit the iron plate. Big bore maker, Gary Barnes, did extensive testing of lead balls shot from big bore airguns in the late 1990s. He discovered that all lead balls deform the same when they hit steel plates at the same velocity. So a .32 caliber ball and a .50 caliber ball both flatten by the same amount when both hit the plate at the same speed. From this he created Splatology — the science of determining the terminal velocity (velocity at the steel plate) of a lead ball by its appearance. If you follow the link, you can read that article.
There is a quiz at the end of that report. You can take it if you like and find the answers at the beginning of the next blog.
From Splatology we know that the ball from the Perkins gun hit the iron plate 100 feet away at a terminal velocity of 560 to 580 f.p.s. So the muzzle velocity had to have been higher — perhaps 625-650 f.p.s. In other words, we can accurately know the velocity of a shot taken nearly two centuries ago! That is the upper end of power for a big bore airgun from the past. But wait — there’s more!
Velocity of the big bore airguns of antiquity
One more point before I get to the air pressure at which these antique big bore guns operated. The Perkins gun was more powerful than most airguns of its day. That means that the velocity those other guns generated was also lower. However, some of the Perkins gun’s velocity was offset by the fact that it was firing a continuous stream of bullets, where the airguns fired but one shot at a time. And some more velocity is given up because the Perkins gun used steam and not air. Air is thinner than steam and flows faster through a valve. So, even though the steam pressure in the Perkins gun might get up over 900 psi and the air pressure in true airguns of antiquity does not go that high, the muzzle velocities of the best airguns are very close to those of the Perkins gun — closer than the difference in pressures would suggest. Let’s take a look at what they worked with.
Available air pressure
There are many accounts of vintage and antique airguns operating. Most of them are unsubstantiated by facts — either in the articles or from tests that have been run to prove or disprove the claims. So, in 1998 Dennis Quackenbush approached me with an idea. Why not create a couple hand pumps that were similar in all respects to those of antiquity and test them to see what they could do?
We did just that and I published the results in Airgun Revue Number 4. And I republished an abbreviated version of that article in a three part blog report in 2008. There is far too much detail to cover here, but in that series you will discover that Dennis and I proved that the hand pumps of antiquity could generate from 750 to 850 psi — though 850 was really pushing the envelope. Theoretically it is possible for a hand pump from that time to generate pressures up over 1200 psi, but to do so the pump’s piston has to be very small. The number of pump strokes such a pump would require to fill a reservoir to that kind of pressure becomes enormous.
Suffice to say we now know that the antique big bore airguns operated at air pressures ranging from 450 to 800 psi. The earlier guns (and pumps) from the years 1600 through 1800 probably operate at the lower end of this scale, while the guns and pumps made at the end of the 19th century are at the higher end. That means whatever velocity those antique airguns were able to achieve had to be achieved by air pressurized within these limits.
You have read in this blog that velocity is achieved in a pneumatic gun by the length of time the valve remains open and the length of time the air has to push against the pellet, which is the barrel length. Only when both of these things are optimized does the air pressure come into play. So valve dwell time and barrel length are more important than the available air pressure. If you need a refresher on this concept or if you are a new blog reader and missed this discussion, look at this report.
Why this is important
Someone might look at these references and ask why it’s so important. Who cares how a big bore airgun operated in 1715? I think the answer is — you care. Or you should.
If you know what is possible with just a puny amount of air pressure in an airgun of the right design, you’ll know a lot about pneumatic airguns in general. There are airgun designers today who are building guns that use pressures of 4500 psi and more. They do it in hopes of getting more from the gun they design. But I would ask them this question — more what? More accuracy? It doesn’t work that way. An Olympic target rifle that runs on 3000 psi is just as accurate as one that runs on 4500 psi. Yes, there are several models in each category.
Does higher air pressure give you more shots per fill? Maybe — but how many more will you get? Will your gun get 3 powerful shots where a gun that fills to 3000 psi only gets 2? Is it worth the effort to find an air supply that can fill up to 4500 psi — knowing that you are limiting the number of places that can supply you air at that pressure by a factor of at least 10? When the Benjamin Discovery was launched it demonstrated to the world that air pressure is not what makes an airgun work well. It runs on a fill of just 2000 psi, yet still gets 1000 f.p.s. in .177 caliber.
Do you think greater air pressure gives you more power? Maybe that’s not important. We already have 500 foot-pound rifles shooting all the way through 1500 pound bison – how much more power do we need? Ask any big bore airgun hunter about bullet penetration and they’ll tell you that unless their bullet strikes a major bone it’s not staying inside the animals they shoot.
What I am saying is there is great value in knowing how these antique airguns worked. Knowing how airguns of the past operated gives us the foundation to design them for the future.