Episode 93: Confederate Steam Gun

Air Date: December 5, 2007

The Confederates successfully created a working steam powered machine gun that could fire bullets using centrifugal force.


The Mythbusters first tried to confirm whether a steam powered machine gun in fact existed. A Civil War weapons expert confirmed that the weapon actually existed and had the blueprints to prove it. However, the gun’s lethality and effectiveness were unconfirmed. They then constructed a steam gun based on the blueprints they received, with a pair of water heaters providing the steam to spin the barrel. On their test run, they fired a single round which struck the gun’s steel safety shield, creating a deep dent which could potentially cause lethal damage to a person. Satisfied with the test run, the Mythbusters took the gun for full scale testing. They tested the gun based on three major factors: a range of 500 yards (460 m), a rate of fire of 400 round per minute, and the fact that the weapon had to be lethal. The gun performed well on the first two criteria, firing five rounds per second at a range of 700 yards (640 m). However, the weapon lacked any lethal force at ranges beyond point blank, and was not very reliable in terms of delivering the bullets to the targets in an effective manner. The Mythbusters concluded that as a concept and a machine, the steam gun performed perfectly, but as a weapon, was too unreliable and impractical.

Through mental or physical means, a person can fool a lie detector test from a polygraph machine.


In order to make the test results genuine, Tory and Grant were instructed to steal money from a safe while the innocent Kari was used as a control. Also, they were promised a reward (first class seats on the next Mythbusters trip) for beating the test and a punishment (cleaning and waxing the entire crew’s cars) for failing. During the test, Tory attempted to use pain to hide his lying while Grant tried to focus his mind. However, neither of them could beat the polygraph. While they both failed the test, the Build Team decided not to rule out the possibility that there are people out there capable of fooling a polygraph.

A person can fool a lie detector test from an FMRI, which measures brain activity.


To set up this test, all three Build Team members had to steal something to fulfill the conditions of the myth. Each member had the choice of stealing either a ring or a watch and then underwent a lie detector test while being scanned by the FMRI. Like before, there was a reward ($1000) and a punishment (a trip back to San Francisco via bus; a 3,077-mile (4,952 km) trip) if they passed or failed the test. Both Tory and Kari tried to think happy and fearful thoughts while Grant tried to keep his brain active for the entire test. In the end, Tory and Kari both failed the test while Grant managed to fool the FMRI, making the myth possible.

A person can repair a fuse box by wrapping a burnt-out fuse with tin foil.


Adam took some tin foil from a chewing gum wrapper, wrapped it around a burnt-out fuse, and demonstrated that it could indeed work in a fuse box.

(This myth was a promotion for the upcoming MacGyver special.)


  1. waren boyd says:

    I believe u have purposely not tried the bullet ricochet myth. but if not I would really like to see and know for myself. I think it either pierces or disincarnate not ricochet please respond at least big fan sincerely Waren Boyd

  2. Christopher Treptow says:

    Your steam gun was not daedly. If you were using rubber balls as bullets that was the problem. You should have gone with metal balls

  3. Bradley Holt says:

    The repairing of a fuse with metal foil is always possible, the problem is that in case of a fault the fuse should be the first thing to burn out to safeguard the circuit. anything metal will do the job including a pin or nail etc. It’s still very dangerous and shouldn’t ever be done.

  4. Russell McManus says:

    You stated that the gun would not kill. Steam at 40 atmospheres has more power than gunpowder at 500 atmospheres and higher. The design was poor compared to an earlier English Steam Gun.

    Jacob Perkins 1824 “Steam Gun”. 300 bullets per minute. Balls of one ounce weight were propelled at 35 yards through an iron plate one-fourth of an inch thick; also through 11 hard planks one inch in thickness placed one inch from each other.

    I have the plans and history of this gun if you want to see it and it will kill. There is a problem though of waiting until the steam pressure builds up before you can fire it. In battle you would need instant rapid fire.

  5. dude says:

    fMRI not FMRI.

  6. Jim says:

    The problem with this gun was projectile velocity. At 2000 rpms the projectiles only had a velocity of about 250 fps. Most handguns fire at three or more times that. If the barrel was extended a higher velocity would be achieved. The same could be accomplished with higher rpms. Another way to increase lethality would be the use of lead instead of steel shot.

  7. caleb says:

    We have an electronics kit at home and when the fuse went out, my older brother used a paper clip to bypass it.

  8. Tiexandrea says:

    while everyone was concentrating on the steam gun, i looked more into the polygraph testing myth. i honestly believe that it kinda fell short.

    the mythbusters/buildteam/researchers might have forgotten that there might be (truthfully or mythically) certain professions that are trained to lie and beat the polygraph test by necessity, such as undercover police officers, spies or even the marines. or they could throw in some politicians, telemarketers and used car salesmen. i honestly believe that the episode would’ve been more informative if they tested the polygraph with those types of need-to-lie-to-live professions. it would’ve been really interesting.

    also, if they were loyal to their drive in “replicating the results” after a supposed bust, they should’ve tried the polygraph test in its absolute worst case scenario. picture this — if a polygraph test was administered to a person in the outdoors, in a relaxing environment, or in the safety and privacy of their own home, would the polygraph still be able to do its job properly? and how properly? and what happens if you do it to a child? ^_^

    mythbusters, i love you guys, but you have to understand that a passed/failed polygraph test is often the difference between guilty/innocent, between job/jobless or between life/death. i’d understand if you won’t want to revisit, but it could’ve been better.

    and my sympathies for Kari’s bus ride.T_T

  9. ed says:

    Read the stuff on the web about control and relevant questions and what to do in each case then let the team practise those principles on a polygraph for a day and then redo the tests.

  10. Mel Goldberg says:

    The reason you Confederate cannon did not work is because the ball was in too loose.You needed to pack the ball tighter so that no steam could escape around the ball which would force the ball out with presure.

  11. Mel Goldberg says:

    Your cannon did not work because there was not enough seal areound the ball letting the presure out.Barreel has to be packed tight.

  12. Thomas says:

    I dont agree with busted for the steam powered machine gun because you used rubber maybe if you used metal and it should oh worked. And i think too much steam escaped the barrel.

  13. FB says:

    Penn and Teller claim that the lie detector can be fooled through tightening and releasing the sphincter muscles. However, their “tests” were not as rigorous as Mythbusters’ tests tend to be. Would be interesting for MB to do that test more scientifically.

    • MSpears says:

      Penn and Teller are right (mostly). You can’t really “fool” the lie detector, but you can make the test inconclusive, by just clenching your arse. It drives your blood pressure up, thus invalidating the test.

      Unfortunately, that’s why they started giving lie detector tests with the subject sitting in a chair where they were reclined at an angle where it is not possible to clench your arse tight enough.

  14. Mike says:

    Busted for the steam cannon. Not sure. What was the material of the ball? smaller ball could maybe do better penetration. And to people who think about steam in the cannon. guys… there were no steam in the cannon. It was the centrifugal power that throw the ball.. not steam itself. but I really think that a bit smaller ball. and longer barrel could change everything here. double the barrel length and wow…

  15. Kate says:

    I think that for the lie detector test you should have tested someone who is used to thinking on their feet, like a improver. Your results may have been different.

  16. Ashley says:

    I heard about raising the emotions on the baseline questions slightly. You have a stronger reaction to “what’s your name”, then “did you steal the money” seems like the truth because your truths register higher.

  17. Tim C-Squared says:

    I have discovered the fault in the Steam Machine Gun. The muzzle was too short and the projectile release mechanism (PRM) was…well…nonexistant. First, the muzzle should be extended to 2.5 feet, with the PRM no more than six inches from center of muzzle rotation. Now for the PRM. At 2000 rpm the rotational period is .03 seconds. Thus the PRM needs to load each projectile within that amount of time. Once released, the projectile experiences accelleration forces due to spinning. This starts at 22000 g’s at six inches, and ends up at 131000 g’s at the exit end. The average accelleration is 88000 g’s, resulting in an exit velocity of 468 fps. This copares favorably with slower .22 caliber and much better with the 250 fps test result. Double the muzzle lenth gets 700+ fps. Double the RPM’s gets 800+ fps, but shortens the cycle time unless you use more than one cycle to fire (so, if you use a two cycle fire sequence, the cycle time is unchanged).

    RPM’s that work this quickly are well within the technology of the mid 1800’s. It may seem that the original blueprints may not have included this mechanism, remember that even Leonardo’s plans were filled with errors to preserve “intellectual rights” and so the plans you saw may have been deliberately omitting this detail for that reason.

    • Lucas` says:

      Everybody is talking about the length of the barrel needing to be longer. That, would make the gun more deadly…… I mean we could make it 3 feet long and end up more with quite a velocity, but the Mythbusters were sticking to the original Confederate plan. I do see a problem with the design though. The drop of the ball needs to be timed correctly. If the ball is tossed in and makes it’s way to the “protective shield” on the outside, it will contact the shield sending the ball back into the barrel and then out, losing much velocity or roll along the shield to the point of exit losing any of the acceleration that the projectile would have gained in rolling down the barrel. Think about how much energy was wasted when the ball was denting that shield. The only thing that throwing multiple balls down at once was accomplish allowing a sacrificial ball to hit the shield, but the other projectiles were still right behind it and had already lost acceleration.

      It appeared that the geared device that Adam was working on was for this purpose, but it was not adjusted correctly. It Should work similar to a WWII aircraft machine gun connected to the crankshaft that times it just right as to allow the bullet to fire between the propeller blades and not hit one.

  18. Roger-W says:

    Was the myth on the steam gun that they successfully built one or that it was leathal?

  19. Victor says:

    Hey, the projectile in the steam gun is not pushed by the steam pressure, so the bullet in the barrel don’t have to be tightly fit. But as mentioned by others, maybe you can lengthen the barrel, or use the lead ball.

  20. Victor says:

    Oh! By the way, did Kari and Tory really took a bus back to San Francisco?

  21. Drew says:

    Here’s the way to beat a lie detector, believe your lie. I’d like to see what would have happened if they had believe they were given the money by the envelope they read, instead of took, or stole that money. It’s a iteration of the truth really, and it’s all a matter of perception. And criminal minds can be convinced they did something right…

  22. felixnoir says:

    If I wanted to beat a polygraph I would use a lawyer and a scientist. The reason is that there is absolutely no convincing scientific evidence that polygraphs are worth a rat’s ass. The Soviet spy Abell beat polygraphs several times.
    In an emergency I once replaced a fuse with tinfoil. Very dumb and dangerous thing to do. However, I don’t think you would need much current to cause the tinfoil to fail.

    I love Mythbusters, but there does seem to be one thing lacking. If they did some basic internet research after getting their results, they might well find they are wrong in some cases or there is other research that impacts on their results.

  23. Donovan Haxton says:

    The Civil War steam powered machine gun still exists. It is rusty, covered with bird dung, and the steam engine is missing.However, it is still some what intact. I have about 10 JPG photos that I have taken of it. If you are interested please send me your e-mail address and I will send them to you

Leave a Reply