What is the limit of a spring-powered gun? The recoil speed is limited ultimately by the speed of transverse waves in the material, which in turn I assume is probably related to the speed of sound in that material. In any case, the best spring material would probably be high-qual steel. Since E=(1/2)kx^2, I would also expect a spring with a lower k constant and stretched a further distance from the equilibrium point to be more powerful in accelerating a projectile than one with a high k constant and stretched less. Most conventional firearms have nozzle speeds of 500-2000 m/s. I was wondering if any spring-powered device can match or exceed these speeds.
Well you see, the sucky thing about spring powered guns is that as the spring stretches out back to it's original length when you fire the bullet, the force exerted on the bullet decreases. I believe you know Hooke's law right? So if you want a reasonably powerful spring powered gun you're going to need quite a long spring, even if it's already very stiff. You'll also need to change your springs very often. They tend to wear out quickly when being smashed around in the breech of a gun a supersonic speeds.
Well, let's take a look at what what 'spring powered' guns are available right now. Air guns. They use a compressed spring, to drive a piston, and the compressed air in the piston pushes on the projectile. Muzzle velocities can be supersonic, so just over 300m/s. This gives practical muzzle energies of around 40ft.lbs For practical purposes, springs with lesser K are used, as they are easier to cock, and provide a more gentle recoil. Although this gives a 'lock time' problem, that there is a delay between the trigger being pulled, and the projectile leaving the barrel, while the spring unleashes it's stored energy. It's a compromise. The good thing about spring piston airguns though, is that the compression of the air in the piston slows the spring down, softening the crash at the end of it's travel. It's a lovely, simple, and elegant solution.
Not all spring-piston guns use coil springs. The Theoben guns (and the licensed model from Weihrauch, the HW-90, and its US/Beeman counterpart, the RX/RX-1/RX-2 rifles) use a pneumatic ram filled with compressed gas. The Weihrauch models use a ram that has a larger-diameter shaft, and one side-effect of this is that the cocking effort is not even over the whole (barrel-cocking) stroke. The higher-end guns that Theoben themselves sell use an improved ram, with a smaller shaft diameter and filled with gas (air) at a higher pressure (~900 PSI vs. 300 PSI for the HW-90 gun). The old Beeman literature used to claim that the lower-grade pressure would peak at around 450 PSI when cocked, where the higher-end guns would only rise to 1100 PSI. But this also means that the higher-grade rams have a more-evenly sustained exertion (both in cocking effort, and in pushing the pellet) over their stroke as well. As an owner of a Beeman RX rifle in 177 cal; I don't have a chronograph but the regular maximum ram pressure is around 23.5 BAR, and at around 15BAR pellets won't make it out the 19-inch barrel. Also the gun fires very smoothly at lower pressures, but when you pump the ram pressure up near maximum, it vibrates a *lot* when fired. I have mine at around 20 BAR and rarely put it beyond that, usually only when someone wants to shoot it at maximum velocity. The 50-lb cocking effort is rather off-putting; they don't shoot it very long. If you pump it up to 24+ BAR, it will crack the sound barrier (1150 FPS), but smokes the piston ring a bit. ------ The "highest velocity" question is rather beside the point. The problem with spring-piston arrangements is that they vibrate a lot as the spring/ram pressure rises, resulting in poor accuracy. Also if the pellets exit at supersonic speeds, they get buffeted a bit as they decellerate back down through the sound barrier, after only a few feet from the muzzle. So it is generally accepted that transonic pellet guns are really of questionable usefulness, as their accuracy is poor. As of a couple years ago, the Theoben Eliminator was the highest-powered production spring-piston gun, at around 27 ft-lbs for .20 caliber. It was available in .177 for only a very short time if at all. At its highest power setting it would drive pretty much every regular pellet supersonic, and wasn't accurate. Considering what it costs ($1200 US or so) poor accuracy isn't exactly a good deal. ---- There was one that could shoot higher speeds; that was the Weihrauch Barrakuda. This was a coil-spring piston rifle that had an augmentation system for optionally injecting a bit of ether into the chamber during cocking. The ether would diesel and the claimed muzzle velocities were 1400+ FPS in .177. These rifles came out during the 1970's and were very expensive even back then, they are considered rare collector's items now. It'd be interesting to see what they'd really do (through an accurate chrony) but I kinda doubt that anyone who owns one is still firing it much, or even at all with the ether injection. ~
The point is that there are some tradeoffs between using a gas-ram vs. a coil spring, but the Theoben Eliminator has been the most-powerful spring piston gun since it has been introduced. The most-powerful spring-piston airgun made does not use a coil-spring at all. And even at that, it only puts out about 27 ft-lbs of energy, in .25 caliber--and depending on pellet weight of course. What spring-piston gun puts out 40? I think perhaps you saw the PCP guns.... ~
This is an excellent assessment, actually. I see why they don't go to extremes with springs now. I wonder if its possible for a spring to go supersonic without having these vibration problems.
Er, Scooter, hello, planet earth calling? The thread is called "Limits of spring-powered guns". So talking about gas-rams is rather tangential. And Facial, yes, springers can easily go supersonic, and vibration isn't really an issue for well tuned air rifle.
Guns have this certain limitation: they're very good at TAKING life, but not so good at GIVING it back.
Rest assured: I am a peace advocate. However, guns have many other uses besides killing living things. I will not even hunt animals.
Quite so. The speed of sound in high-qual steel can reach almost 6km/sec. That's pretty promising velocity potential if one can make a spring with a high lead distance and number of threads (somewhat like a drawn out multiple helix)
An alternative to spring, but with a lot more punch http://www.answers.com/topic/resilin?method=8 The link is slow so wait for 2 minutes to complete loading.
Hi there, can anyone tell me what is the stroke length and draw weight of a gas ram fitted on a Theoben Eliminator?
you are right...but i already asked theoben and they refused to submit any data.. so can someome indicate what is the stroke length and draw weight of a mainspring then, fitted in an airgun that yields 24 ft/lbs of energy? any kind of info is much appreciated
