Catapult guns and velocity

by Tom Gaylord
Writing as B.B. Pelletier

A history of airguns

Sharpshooter
Sharpshooter pistol uses rubber bands to launch a .12 caliber lead ball. Other catapult guns were as large as .43 caliber!

This report covers:

  • You know catapults guns
  • More power doesn’t mean higher velocity
  • Why a limit?
  • What is the limit?
  • Crossbows may be faster — but…
  • What about stonebows?
  • Conclusion?

You know catapults guns

Over the years I have written several reports about catapult guns . The Sharpshooter shown above and the Bullseye pistol that proceeded it used rubber bands to launch their shot. But the Johnson Indoor Target gun used surgical tubing. And a don’t really know for sure what the .43 caliber Hodges gun of the 1840s used but I suspect it was natural rubber bands. The point is, catapult guns have used many different power sources.

Johnson Indoor trainer
Johnson Indoor Trainer uses surgical rubber tubing.

More power doesn’t mean higher velocity

Most people equate the strength of the elastic bands with velocity, but with catapult guns it doesn’t work quite that way. It is possible to increase velocity by adding additional bands or stronger bands to a point, but once that point has been reached, no more velocity is possible. There is a close correlation between catapult guns and spring-piston guns in this respect. though there are also a few significant differences. For today,  let’s stick with catapult guns.

I discovered during testing of the Sharpshooter and Bullseye pistols, that by adding additional rubber bands I could boost the velocity from around 100 f.p.s. all the way up to about 170 f.p.s. Then it stopped rising and I couldn’t fit any more rubber bands on the guns. If I worked at it, there is probably 30 more f.p.s. to be had, but that will be the limit.

Why a limit?

This is the crux of the question, and it also applies to the metal springs, found in conventional pellet guns. The larger a spring becomes, the greater its mass. The greater the mass, the slower that spring operates. It will push more weight, but it will do it slower. That defines the velocity limit of a conventional spring.

A stronger but slower spring will push more weight at a given velocity. In some catapult guns where the shot size is limited by te gun’s design, you have to find the optimum spring size for your projectile. In other catapult guns where there is greater latitude in the projectile size and shape, a larger spring means greater weight can be pushed. A gun like the Hodges will benefit from using the biggest ball made from the heaviest substance. That would be a .43 caliber ball made from pure lead.

Hodges catapult gun
The Hodges catapult gun from the middle 19th century shoots a heavy lead ball.

Other catapult guns may allow the use of different-shaped projectiles. This is where the speargun comes from. And some guns may be convertible to shoot either spears/arrows or round balls. Match the projectile to the application. But with all of them the size of the spring — be it a rubber band or a thick natural rubber cord — determines the velocity. More power does not mean more speed.

What is the limit?

For many years I have written that the Hodges was capable of taking boar-sized wild game, based on an estimated velocity of around 350 f.p.s. Well, where does that number come from? It came from a remark made by Larry Hannusch, when I was talking to him at an airgun show about his Hodges gun. I asked him if he ever shot his gun and he said he had. But he never really chronographed any shots from it. He had loaded both sides of the launcher with rubber tubing, one band at a time, until the steel arms of the launcher appeared to be stressed. That was where he stopped. When I pressed for a velocity number he rolled his eyes and said, “I don’t know. Maybe around 350 f.p.s.?” It was a best guess.

The point is, no velocity testing of a Hodges guns has ever been done — as far as I know. But there has been testing of the catapult concept by itself. In his book, Man-Powered Weapons and Ammunition (copyright 2005), by Skyhorse Publishing, New York, Richard Middleton did a test to find the limits of several catapults. While doing this I believe he stumbled upon the fundamental fact that all catapults have a limit.

That limit seems to be around 250 f.p.s. It seems that nothing can be done to increase that limit. If more elastic bands are added the gun will launch heavier projectiles just as fast, but nothing will make them go faster. Maybe this should be called the elastic limit or barrier?

Middleton did not actually conduct his tests to find this limit I am describing; but all of his tests of catapults seem to end just shy of 250 f.p.s., save one. A condom firing a chickpea was able to reach 270 f.p.s. — or so it was claimed. While Middleton never states that 250 f.p.s. is the practical limit of a catapult, I am suggesting that it is, based on all of his results.

Just as additional mass in a coiled steel mainspring actually slows the spring down, so does adding more elastic material to a rubber band or surgical tube. This mass/accelleration ratio is what defines the limit of a catapult.

Crossbows may be faster — but…

I say that crossbows may be faster than other types of catapult guns, but their upper limit seems to be around 425-450 f.p.s. That’s more velocity than ball-shooting catapults are getting, which makes crossbows more efficient. And obviously I’m talking about crossbows with conventional limbs and a string — not airbows.

What about stonebows?

Some of you are aware that there are such things as stonebows. They are crossbows designed to shoot stones or balls. Middleton did test several stonebows, though his tests were by no means comprehensive. The max velocity he got hovered at just over 200 f.p.s. So the stonebow falls well in line with the elastic limit.

Conclusion?

I conclude from both Middleton’s writings and my own limited tests that 250 f.p.s. or thereabouts is probably the limit that a spring-powered gun can achieve. If I am right, we now know something important about airgun design. If I am wrong, whoever disproves me will advance our understanding and knowledge.

The bottom line is this — catapult guns are slow. And they will always be slow because of the limits of the springs that power them.

49 thoughts on “Catapult guns and velocity




  1. BB,

    I did a little calcumalating and that Hodges would only be putting out a little over 18 FPE. However, the mass of the projectile will allow it to carry more energy further. Kill a hog with it? It had better be a very well placed shot or you are going to have one very angry boar on your hands.


  2. Hi,
    I am a slingshot enthusiast, and did some experimental research on that matter. The results can be found on my webpages (www.slingshot-shooting.de and http://www.melchiormenzel.de)

    In a nutshell..velocities over 450 fps gave been achieved with rubber powered weapons. What counts is the rubber geometry ( i.e. Tapering, using flat bands) and mainly the draw length, which can only be so much in a slingshot gun, unless you don’t care about handling a huge gun. Very high speeds are also bad for the rubber bands lifespan.
    Increasing strength of the bands does not increase velocity, but allows you to shoot a heavier projectile at the same speed. The contracting bands (without projectile) have a maximum speed, and you will never exceed this limit.

    There was a time around 1900 to 1950 when crossbow, firearm, airgun and rubber powered guns battled for the field of parlor \ plinking \ target shooting. The airguns won this struggle with flying flags, crossbows found their niche in more powerful applications and rubber powered weapons retreated back to slingshots, where their compactness and low price gives them an edge.





          • Yes, this is comparable. I want to add that the longer rubber bands are kept under tension, the lower will your velocity be. This, together with the need to constantly replace rubber bands, makes the “slingbow” have a hard time against its direct concurrent, the crossbow.


          • Yes, indeed. Acceleration is defined as increasing velocity. While learning to drive, I found that keeping constant pressure on the accelerator meant that I kept speeding up! Also, the definition of spring force is

            F = kx

            where k is the inherent tension in the spring and x is the distance it is pulled from equilibrium. So that bears out the two arm technique.

            Matt61


  3. Hi BB, I also mess around with slingshots and have hunted sucessfully with them. As Mel notes ,the heavier bands launch a heavier ball. There is also a big difference in performance on game between a 1/2″ lead ball and a 3/8″ steel ball. This notion of shooting stuff at long range is a recent one . A hundered and fifty years ago , most stuff was killed at very short ranges. The new airbow from Crosman is a important advancement of another type of weapon that is similar to a crossbow with higher velocity .The high velocity doesn’t really enhance the practical range of the device , or the effectiveness on live targets. The convience of using a PCP platform that can be decocked, and that avoids the heavy physical effort of cocking the bow is the advantage with that. I would rather use any airgun of reasonable power, than my Trumark for hunting rabbits. The only advantage with the catapult / slingshot, is that it is cheap and portable and could be improvised using simple materials and rubber bands from the office supply store



  4. David, BB– I saw a picture of the RWS Mauser 98 on the hard air gun website. It is based on the RWS 460. I have read a few negative comments about the 460 ( pins and other parts breaking) I have also read some negative comments re Umarex customer service and repair and warranty. I may have one in the near future. I am waiting to hear from Umarex re repairs to my 1911. These comments may keep me from buying a RWS 98. I collect military trainers and would want to buy one, if not for the above comments. I would like to hear from our bloggers re their experience with with the 460 and Umarex repairs. Ed


    • Ed,

      Might the Diana Mauser K98 be based on the 430 instead of the 460? I just found a pic of it below a Diana 34 Classic, and the K98 is noticeably shorter than the 34. Both the 34 Classic and 460 are 45 inches, whereas the 430 is 41 inches.

      Michael


  5. B.B.,

    As Scotty exclaimed, “Cap’n, I canna break the laws of physics!”

    When I read your Shot Show report about the almost 30-foot-pound Hatsan Carnivore, I was reminded of a series of reports you did from six or so, on the “Steel Dreams” springer experiment and how it failed to get a lead .22 pellet to supersonic velocity. As I recall the biggest hurdle it failed to clear was its heavy spring and piston. While I suppose that by now there are a handful of .22 springers than can (barely) launch an 11.9 Hobby faster than sound, PCPs have made ultra-magnum springers a slowly dying breed. I suppose a high tension spring of a lightweight alloy or synthetic material could do the trick, but such a springer would probably not ever be marketable enough to justify the R&D.

    Whatever happened to the Steel Dream rifle?

    Michael




        • Reb,

          You gave me just the excuse I needed to reread B.B.’s excellent report (and the URLs are below). I wonder how different the experiment might have turned out if a) the spring were replaced with one of less mass but similar tension and length, b) the piston were replaced with one of slightly less weight, c) the piston seal were of a parachute design, d) the barrel were a proper fit for .22 air rifle pellets, and finally, if e) the barrel were shortened to reduce the drag of the unnecessarily long barrel Steve Vissage used. The fastest it shot 14.5-grain Eley Wasp pellets was 776 f.p.s. With the refinements I described, I would not be surprised if it could shoot .22, pure lead 11.9 grain RWS Hobbys at 1050 fps or so. Granted, there are stock springer air rifles for sale now that CLAIM to do that, and perhaps some can, but I have doubts. Webley Patriot? Hatsan 135? Stoeger X50? Gamo Extreme?

          I’d love to get my hands on that Steel Dreams rifle.

          Reb, here are the two URLs:

          /blog/2008/09/steel-dreams-part-1building-a-more-powerful-spring-piston-gun/

          /blog/2008/10/steel-dreams-part-2-building-a-more-powerful-spring-piston-gun/

          Michael


          • Michael,

            Thank you for those links. Fascinating. For anyone that has ever dreamed of making their own custom airgun, the links are a must read.

            Only 3 were ever made and the owner/builder kept 2. BB got the 3rd. I do not know if I could have parted with it. Talk about limited production. I could see someone making a very substantial offer for it though.

            Thanks, again, Chris


  6. I’m wondering about the reason behind the theoretical limit to catapult speed. It is obviously nothing to do with the projectile itself and its terminal velocity, so it must be due to the catapult itself. I’m supposing that the limit must apply for a specific material like rubber or the elastic tubing that is often used for this purpose. Are the different kinds of elastic that uniform? In theory, if someone created a new kind of elastic just as they are producing new kinds of synthetics all the time (“Plastics, Ben. Enough said.”) it would change the velocity limit.

    Gunfun1, ha ha. That is a good one. I might be there already. As a matter of fact, I’ve been reading around in psychology and discovered the darnedest things. There is a case study you can Google about a person named Ann Winsor who believed that an alternate personality had taken over her right arm. She even named it Old Stump. There were indications in her favor. The arm was insensitive to biting or pricking which she did to try to bring it back under her control and seemed to have a mind of its own. But it was completely benign and in some respects improved on the original. Anna was an unstable person given to self-destructive behavior, and the arm would intervene to protect her. It communicated by writing and drawing pictures, showing a rational and educated personality. It also never seemed to sleep and would watch over Anna as she slept while continuing to write and draw in complete darkness.

    So, what does this have to do with shooting? Imagine if the arm had fired a gun! If it could draw in darkness, it would be better than a Trackingpoint scope. I wonder if this is a version of the mysterious Jaws of the Subconscious that somehow takes control and gives you that perfect shot. This is actually not so different from the Bourne Identity where the ordinary man is possessed of superhuman abilities. I think the appeal of the film is the wish for everyone to have a superspy inside them. Granted the Bourne character was the product of extensive training. (“You are a malfunctioning 30 million dollar weapon, soldier, and that is not acceptable.”) But the potential had to be there to be trained. So maybe everyone has a bit of Jason Bourne or Old Stump inside them to be cultivated. Further proof that shooting relates to everything.

    Fido, interesting about bayonets for riot police. While their purpose seems to be kicking butt, I believe that they are really supposed to disperse rioters which is to say defuse violence rather than increase it. Bayonets would constitute deadly force and make rioters even angrier, I suspect.

    Matt61



    • Matt61
      Yep that is amazing ain’t it. And we only use a portion of our mind. There was a movie that came out a while back of a person that was able to use more of their brain than normal. I believe a girl played the person in the movie.

      Never did get to see the movie but would like to if I could just remember the name of it. See I can’t even remember to use the part of my brain I’m suppose to be able to use. Let alone tap into other parts of it. 🙂

      Just like dreams. You ever have those dreams and you wake up and go wow. Like places you know you never been but look so real. Or cars or motorcycle’s that ain’t never been made. But can see every detail of the engine or parts of the interior and such.

      The mind can definitely do things. They say the more you think about doing something like opening a biusness. You start thinking about all the things involved and before you know it you talk yourself out of doing it. Or it can work in positive ways like when shooting. If you set your mind to making let’s say that long distance shot. And you know your gun and how it shoots. Basically confident from making other shots. You will probably make the good shot. But if you think right off the bat that’s too far of shot then you probably are going to have problems with the shot.

      I know when I start second guessing my hold over or windage I’m suppose to use at a certian distance I usually miss. Even when I know I made that shot before but didn’t follow what I knew had worked. Yep the mind can mess with you if you let it.


  7. B.B.
    More experiments: Using the Pellet and BB Gages and indirect measurement with lead BB’s, the barrel of a Crosman 760 seems to be only .03 mm (.00118 inch) larger than that of a Daisy 499. If anything the Crosman barrel seems to be more ridged and I can’t detect any difference in uniformity. Premium
    Steel BB’s seem to fall through the Daisy more slowly when the breech end is covered with a finger tip but not by much. (Both barrels out of the gun.)
    Speculation: (A) if Crosman made a premium BB matched to the 760 barrel the results might be very interesting. (I tried 3 760 barrels including one from the 90’s and they
    seemed very close.)
    (B) Oil has only to fill a .00118 (divided by 2) gap to be effective in increasing accuracy.
    Fido3030


    • Fido3030,

      Very interesting. Comment (B) was good. One question,…what allowed you to determine the exact size of the barrels? No doubt your bbgage played a part. I would guess, and it is only a guess, that you found the exact size of the bb that (would) pass through the barrel(s) and the one size bigger that (would not) pass through. Hence,.. the “indirect measurement” comment in the first sentence.

      Cool stuff. Chris


      • CHRIS USA
        I have lots of brands of lead BB’s and fortunately (in this case) they vary in size. I tried Gamos until one was a slip fit in the 499 barrel. Then I tried H&N 4.5 mm until one was slip fit in the 760 barrel. Then gaged both and found them .03mm apart in size. There are instruments for measuring barrels but I don’t have them. This method i think gives pretty reliable results in a smoothbore and is repeatable.
        Fido3030


        • Fido3030,

          That is pretty much what I had thought. (And your bbgage allowed you to it). And yes, I think that is a pretty reliable way to go about measuring the barrels. Nice work.



  8. B.B., a most interesting topic today, because it touches on such a wide area of issues related to systems, physics and the limits reality imposes on our aspirations. That is a good thing and needn’t stop us from trying.

    Thanks to the posters for some nice links to further boggle my math and physics mental limitations. Good stuff.

    I keep learning some things. You mentioned in this blog and in other places that more power doesn’t more speed (or at least not much). In the early ’70s I worked briefly for a man who bought an aircraft manufacturing company. He owned one of their planes. They manufactured one plane, but it came in a single engine and dual engine configuration. What I learned at that time is that the maximum speed of both configurations was very nearly the same, but the dual engine could carry a heavier load. I belief this is analogous to what you said above, and also here:
    /blog/2013/07/why-powerful-mainsprings-dont-always-increase-velocity/

    You mentioned crossbows; here is something dealing the limits of speed with hand drawn bows:
    http://www.outdoorlife.com/features/chasing-speed-fastest-compound-bow/
    They also mention manufacturer’s claim and how they arrive at them. I know for a fact I can shoot a lighter arrow from my bow and get greater speed, but as with air guns, accuracy takes a nose dive.

    Now, for some news from Lake Wobegon (I hope Garrison doesn’t sue me).
    I haven’t gone to the range to shoot a .45 yet but I believe it will be relatively soon.
    I installed a one piece scope mount on the little Crosman Model 3100 .177 and finally have things staying put. I installed the 4×32 scope that came with the Titan. I have been pleasantly surprised with good results shooting Crosman Destroyer pellets out to 20 yards, all in all a better value that a B3, I think. As for kinetic energy, it dents the pop tops from the cat food but does not penetrate. I expect will enjoy shooting it; not that I don’t, but she can’t cock my other two.

    Best to you, B.B.
    ~ken


  9. Good article. The description that more bands will launch a heavier projectile, with no increase in fps, was good.

    Tie that in with the spring of a springer,.. and you had the perfect comparison. At some point, the extra cocking effort is not worth it.

    Mel83 had some good points as well. The one thing that I think can not be compared is,…swept volume. That is where air guns may have the advantage.


  10. BB, Michael, etc—-I just looked at the Mauser Diana Lifter website. The price of the 98 air rifle is 469 Euro, which translates to $508.86.If there are any interested German speaking bloggers, I hope that they will translate this blog. It looks kike a lot of info, but it is in German. This price is comparable to the price of the Diana 460. Ed



  11. BB– The energy of the RWS 98 is 26 joules, the exact figure given for the .177 RWS 460 magnum. In .22 cal the figure is 33 joules. And LIKE, not kike. BB, please change. Ed


  12. Yep why do so many spring gun manufacturer’s use so much spring preload.

    I have taken almost 4″ of preload out of some different brand spring guns with interesting results. And others not that much. But close.

    They shot the same pellet at the same speed. Or even faster on some of them.

    All the extra preload is doing is wrecking the gun.


  13. B.B.

    I guess I don’t understand exactly how these guns work ,but I would think a 3rd class lever would multiply the velocity.

    Picture a gun-stock with a cross member at the front that is rigid.A pivoting arm is attached to each end of the cross-member.They cross each other over the gun-stock in the back and are loosely connected to a “carrier”.The carrier can slide forward on a track along the stock.A trigger holds the carrier in place.The carrier has a tube that fits inside the barrel.A hole in the carrier tube allows a ball to be loaded and a plastic whisker holds it there.Rubber springs affixed to the front of the stock are then slipped over pins on the pivot arms at a third of their length from their pivot points on the cross-member.Now you have a cocked and loaded gun that should give you 3 times the velocity minus friction losses.

    Synthetic sponge on the front of the carrier can minimise the shock of the shot cycle.The pivoting arms must be able to run by each other behind the carrier because they will follow an arc and protrude further as they move.

    Well that’s my idea anyway.Don’t get your tongue caught in there now will you?

    -Tin Can Man-


Leave a Reply