Vacuum Pressure Bazooka

This vacuum pressure cannon is a design unlike any we’ve seen before. At first look it seems to have the components you see in a potato gun. But those use a combustion process to launch the projectile. This instead uses the sudden release of a vacuum.

About three minutes into the demo video below we get a look at the “ignition” system. It’s pretty scary in that a couple of really powerful springs are pulling a collar along the barrel toward your face. This is actually meant to dislodge the plug in the back which is holding vacuum in the barrel. The pressure difference causes a sudden inrush of air which shoots the 1.5 inch projectile out the front of the bazooka.

[Mr. Teslonian] built his own hand powered vacuum pump for loading the weapon. This was done with a pair of PVC pipes that fit inside of one another, and a plunger made from wood and leather. The PVC and wood projectile seals in the barrel using a skirt made from duct tape. After breech loading the projectile and plugging the back of the barrel, he layers aluminum foil over the business end and pumps up a high vacuum. His test firing is not from the shoulder, and he only gets one shot because the slug hit the target so hard it was destroyed. This thing really needs to be vehicle mounted!

[Thanks Ryoku]

39 thoughts on “Vacuum Pressure Bazooka

  1. I think this is a very clever idea. Not at all what I was expecting, as it looked like a combustion or compressed air potato gun. Much less chance of the barrel turning into a shrapnel cloud on firing with this setup.

    Probably not as efficient in terms of projectile velocity; pressure driving the projectile is limited to atmospheric. Combining this with a pressure vessel behind it to supply air at more than atmospheric would give huge improvements in velocity. Even pumping up the pressure vessel to one atmosphere would double the driving force on the projectile. It should be a large pressure vessel though, because one advantage of this vacuum driven system is that there isn’t any pressure drop as the projectile goes down the barrel. Normally, on an airgun with a small, high pressure chamber to store the air, pressure drops a lot by the time the projectile is at the end of the barrel, limiting the achievable velocity.

    A few ideas to improve/simplify this:

    first thing that strikes me is put a lanyard on your plug, so you don’t have to go hunt it down each time. Reduces the chances of shooting someone behind you, while shooting at the target in front of you too. As is, this has a ‘friendly fire’ potential similar to that of a recoilless rifle or bazooka.

    Second, a return spring on the pin that retains the sliding collar would simplify the cocking process too.

    Third, the suede leather on the plug is probably not going to hold vacuum for very long; if you turn or file a groove in the plug to hold an 0-ring, that might make for a longer lasting, smoother opening seal. Same goes for the vacuum pump.

    1. Interesting so something like this?

      I think that could be very effective. However, one major concern I would have in designing something like that would be the valve exiting the compressed chamber to the vacuum chamber. I think it would almost have to be a full width opening otherwise you run the extreme risk of launching your valve with your projectile. Maybe some type of blast gate that can open quickly? Anyone have any idea how those water slides work, where you drop almost vertically? Some mechanism similar to that may work.

    2. Vacuum guns are great for exit velocity because there’s no air drag inside the barrel to slow things down. Regular pressure guns can’t fire a projectile faster than the speed of sound, because that’s how fast a pressure wave will travel, but since there is no pressure inside the tube, nothing prevents the air from rushing in at supersonic speeds and pushing the projectile along just as fast.

      Of course you need to add a nozzle to make the inrushing air go supersonic, but that’s trivial.

      1. Whad’ya mean regular guns can’t fire projectiles faster then sound (in air)?!
        Pretty much all modern conventional rifles fire the projectile supersonic, mostly over Mach 2, some over Mach 3…
        And that railgun BAE built for US navy also has normal air pressure in the barrel, yet that doesn’t stop it from flinging the projectile down range @ Mach 6+ with 33MJ of muzzle energy.

        1. Projectiles can’t achieve a higher velocity than the mach speed of the working fluid. If you build a compressed-air gun, it can’t go faster than the speed of sound in air (ignoring temperature/pressure). If you fire a projectile with a gunpowder explosion, you can’t travel faster than the speed of sound in the combustion gases. This is why ‘light-gas’ guns (that use super-heated hydrogen as their working fluid) are used to achieve super high muzzle velocities.

        2. Compressed air guns can’t fire a projectile faster than the speed of sound, because the pressure wave behind the bullet advances at the speed of sound. The speed of sound changes when you change the temperature and density of the gasses involved, for example, hydrogen or helium may be used as the working gas to achieve high exit velocities, or you could heat them up by a combustion process.

          The point is, that a vacuum gun is capable of accelerating the inrushing regular air to supersonic speeds because it has a vacuum in it, so with a special nozzle you can convert nearly all of the pressure into kinetic energy.

      2. not entirely true. with a long enough barrel the projectile could travel faster than the speed of sound in a vacume and then exit at mach. it would slow past the principal velocity but in effect hold a true trajectory without any expedient methods of stabilization within the barrel.

        rifling was developed to true aim countered to air resistance and has maintained its stature but smooth bore weapons with vastly superior super sonic projectiles maintain vector well past low yield ordinance due to sheer brute force.

        the rail gun being the principal of current research, and of the limits of physics, in the research into the mechanism of propulsion; combustion evacuation is the principal method of reaching any sibilance of super sonic travel. there are even scram-jet bullets (I can’t remember where I found the article but it was a .50 that traveled over 10 miles on the grains of a standard cartage buried in the rear cavity in series to push it along) while a bullet is an ineffective piece of field artillery larger physical properties need be applied to get a shell booking towards distant destinations on the ICBM scale which ballistics of a man portable shell can’t provide (yet)

        1. Rifling was invented because no bullet or barrel is perfect, so they each veer off in different directions, whereas if you spin the projectile it will on average go straight.

          It had nothing to do with air resistance.

    3. rather than arguing the fundamentals I would say that this system would be safer than the bazooka of antiquity if it where engineered with the three phase factors of the plug/vacuum/membrane all engineered into the system relying on the shell to launch and arm it, albeit with a similar range threshold to a WWII spring bazooka.

      i dislike the “practical” applications of such a thing but with a penetrating sabot it could be more reliable than the WWII bazooka because of the launch reaction could be sheltered from the charge until actual impact threw the housing and launch medium.

      I’ll ask you to read between the lines on this comment because I’d rather not explain it and make it easier to engineer than it already is (not a sarcastic comment, I have a “practical” device in mind but I don’t want to share)

      on the authors question of spring tension. I ask how this is comparable to the tension of a WWII allied Bazooka that measured nearly 100’s of lbs. looking at the akimbo pair of 10-15lbs springs I question weather or not these could do [i]that[/i] much harm if properly shielded withing a shell. unless massively fatigued a frame of any measurable strength (even plastic) could prevent a snap/rebound failure, that’s a relatively remote matter of maintenance, inspection and shielding. Even the most rudimentary heat shielding could prevent injury from that particular failure and considering the platform that’s the least of a users hazard’s if this product where to be scaled up…

  2. i have thought of this before but it never left the thought stage because i had no way to seal off the tip of the barrel from vacuum
    i did have a thought to use a loosely fitting plug and hope that there was enough pressure to have the plug fall off
    but then counter strike: source came out and … yeah

      1. na I think its valid, who wants to get the ATF called on you for tinkering in your garage without a diploma from MIT? like anywhere else in society being smart has its liabilities…

    1. This was my concern. The burst disk looks pretty fragile, and if something damaged it he’d fire the plug out the back end… This could be extremely unfortunate, depending on what the back end was pointed at. I’m not sure how you could improve that – any burst disk that’s going to be soft enough to not divert the projectile is going to be fragile. I considered, say, an o-ring at the barrel tip and a steel disk, but even if tethered to the barrel the projectile hitting it and pushing it aside is definitely going to impact your aim.

    2. I don’t think that would really be a large issue, for a couple reasons. First, you need to realize that this system is powered by a pressure differential created on either side of the projectile when the rear plug is ejected. This applies roughly 1 atm of force on the projectile and accelerates the projectile to the end of the barrel. If the burst disk were to prematurely rupture, the differential (which is still acting to propel the projectile in the intended direction) would actually decrease to zero. Only the inertia of the incoming air would lead to the projectile to move backwards, where it would hit the rear plug an be slowed or stopped.
      Ok, so this is assuming the bullet is at the very end of the barrel and there is no volume behind it for a vacuum to develop. Even if there were, the force applied by the barrel volume reaching atmospheric pressure would come on gradually (compared to the intended method of firing). Also, the distance over which the projectile is accelerated is so small that I can’t imagine it would gain very much speed/energy. Remember, work (in this case the imparted K.E.) = force x distance and K.E. = 1/2mv^2.
      Again, hitting the rear plug would drastically reduce or stop the projectile in this case.

    1. you have to recycle those legs from the ironing board somewhere. it would be a willing sacrifice for science. I just hope he hands it to his (survivalist) lab assistant to take one for the scientific team…

  3. At my university one of the introductory experiments that physics freshers do is a carrot cannon that works on this same principal. A length of PVC tube with a T junction at the end is connected to a vacuum cleaner. the vacuum end of the tube is sealed with a couple of layers of foil, the other end as a carrot based projectile inserted and is then covered with a students palm. the vacuum cleaner is then turned on, and the student removes their palm. We’ve managed to get the projectile well over 100m before.

    1. meh, hand made and life hacks are defunct. had to get a HAD mention somehow. backyard bazooka didn’t seem to cover it =P tell me the science behind it isn’t facinating. its a vacuum gun!

  4. But is it really an atmospheric pressure bazooka? At 14.65 psi at sea level the pressure isn’t that high, but the volume tank is F’in huge when used with his ingenious quick release valve. Changes I’d make. find or have made a coil spring that would fit over the pipe the collar slides on, although I’d put a cover over that as well. A recent experience with zip tie failures, I’d use another method of attaching it to the stock. That manual vacuum pump needs a rework so the vacuum is created on the down stroke. I’m lazy and there may be thousands of unable propane bottles around. I’d get as many as I could connect them together to use them as a reservoir and using the the manifold vacuum in my truck engine to draw them down. The need to plug the frond end of the barrel hurts the rate of fire. I think the firing mechanism could be used to yank out a tethered reusable plug after it ejects the rear plug. Finally I think hackers need to discover the existence of pump cups, or at least how to form their own, as they are getting expensive to purchase. While this might be too involved for those in a hurry, but it’s a start in the direction.

  5. One interesting aspect of this is 3D printing. Trying to make a printed gun that copies a standard explosive-based weapon is going to be a zero-sum game for a while yet, since it requires materials that have properties that thermoplastics don’t.

    This, however, is rather different. You’d need to change the design a bit, and finish some parts of it outside the printer, but there’s nothing about it that seems to me to be a deal breaker. Shame he didn’t try using sabots.

    Is there something about firearms that’s sacred? If not, then legislating against 3D printed weapons seems a bit like banning all knives (including kitchen knives).

    Perhaps it’s worth remembering that, contrary to popular belief, Archduke Ferdinand was shot with an airgun, not least because airguns were the most powerful side arms available. This, of course lead to WW1, which didn’t work out well.

    It’s kind of like electric cars. Half of them make a truck look light and sporty. Contrast with electric bikes which draw their inspiration from the latest bicycle tech (exotic design and materials) and the model aircraft world (power storage and management), rather than the Harley Davidson Motor Co., and thus electric bikes are rapidly becoming practical in urban areas, in marked contrast to electric cars.

    Disclaimer: Before any Bros come around to massage my head with tyre irons, I am a Harley owner myself, and know of what I speak :).

  6. For some reason this one’s been sticking in my mind, so I did a bit of back-of-the-envelope sketching and figuring. A few more thoughts;

    Sadly, force on the projectile scales really nicely with increased barrel diameter, but the engineering requirements for the burst disk scale up too. So much for turning an abandoned hydropower penstock or a few miles of concrete culvert into a poor man’s orbital space gun for backyard space tourism.

    Parts count and complexity is excessive on this. The sealing plug and it’s spring loaded pop-off mechanism, which is most of the gun other than the barrel, isn’t necessary at all. In my sketches, the barrel has a burst disk at both ends. The projectile sits in a cut off section of barrel just a bit longer than it is, just enough that the sealing cone is engaged on one end, and the other end has enough clearance to keep the pointy end of the projectile clear of the burst disk. It could even be duct taped to the barrel. Any nudge on the projectile will push it forward into the burst disk. As soon as the point touches and penetrates, the burst disk is going to fail, full atmospheric pressure is going to slam the projectile down the barrel, and bob’s your uncle. the trigger just needs to be a rod that reaches back and gives the projectile a forward nudge. If you had a frame that held the trigger mechanism and had clips for the barrel and the short tube that held the projectile, you could have multiple pumped down barrels and multiple projectiles ready, just clip in and fire.

    You might see a performance increase with a carefully calculated geometry to the entry. The more the flow stays laminar, the less pressure drop you’ll see due to turbulence and the more of that atmospheric pressure will push the projectile.

Leave a Reply

Please be kind and respectful to help make the comments section excellent. (Comment Policy)

This site uses Akismet to reduce spam. Learn how your comment data is processed.