I am writing a Steanpunk novel and am interested in having a "plausible" Union Steam Gun that would help turn the tide in an Alternate History American Civil War.

The gun can be either a machine gun type weapon that is operated by two or more soldiers or a hand held carbine or type weapon handed out to Union Cavalry.

My research found there was a Steam weapon called the Winans Steam Gun, that was also a centrifuge gun. Perhaps ideas on how to modify that to make it more effective.

By, the By, Thanks to everyone who answered my "Quick destruction Of a helium filled airship," question. You all are absolutely amazing, wonderful, creative thinkers. I am so grateful that you all choose to freely share your ideas and knowledge on this site. It is a wonderful tool and blessing for authors.

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    $\begingroup$ Start by watching the correct Mythbusters episode. $\endgroup$ – Zeiss Ikon Sep 16 '19 at 14:18
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    $\begingroup$ Step 1: Assassinate the stakeholder demanding the 'hand held' requirement. $\endgroup$ – Morris The Cat Sep 16 '19 at 15:53

"Plausible", "Hand held" and "Steam Powered" are mutually exclusive terms when you're dealing with steam power in the age of steam.

Steam is big, it's heavy, if you're lucky it's self propelled, and even then the Winans Steam Gun didn't match the power of gunpowder weapons and its accuracy was terrible. If you want steam powered weapons, start with self propelled artillery and work your way up to tanks, but hand held is out of the question.

Traction engines did exist by that point, so having a steam powered base for your mobile artillery is possible. Making the weapon more effective is possible, but with steam it's almost always about boiler pressure, and at that point higher boiler pressure means a bigger, heavier, boiler and a bigger, heavier, furnace.


Let's try a look at the 'machine gun type weapon operated by two or more soldiers', because handheld isn't going to work, and I see no reason to drag the poor horses into this mess. The problem with the Winans Steam Gun is that it's just markedly inferior to rifles and and the Gatling Gun. So let's discuss Gatling Guns.

The Gatling Gun, by which I mean the one invented by Richard J. Gatling, and not the modern guns which bear the classification 'gatling', was invented right before the Civil War, with the intention being to 'reduce the size of armies and show the futility of war', of which it only accomplished one of those things. It had a few unique features, like the 'rotating barrel' concept, letting it fire faster without the barrel overheating, and used a gravity fed hopper. Now, here's the interesting part - it was hand-cranked. And where I see a hand-crank, I see a spot for a steam engine.

In other words, if you hook up the steam engine to the gatling gun, you can eliminate the need for a person to hand-crank the gun and possibly improve the firing rate - though not too much, because at a certain point overheating starts being an issue, but you could work through those problem by increasing the number of barrels (it started at 6) and reducing the caliber of bullet (started at .58), and the increased weight wouldn't be an issue, because it's not hand cranked, perhaps even up to a thousand rounds a minute. (Possibly - the highest it actually got was 900.) At which point it's not exactly hand-held, and would take a team of soldiers to use, and is only slightly better than the original Gatling Gun, but does work. Slightly.

Though if you want, you can stretch plausibility slightly by mounting the thing on a traction engine, add some deflective armor, and you suddenly have an impromptu half-track slowly charging at the enemy. It won't work on uneven terrain, get stopped cold by trenches (which were everywhere), and be a massive target for enemy cannons but just imagine these things tearing through a Confederate charge.

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    $\begingroup$ The Gatling gun, being gravity-fed, could only fire so fast. As the speed of rotation increased, it would either not feed a round into a given barrel, or it might jam. In the case of the former, that would not prevent continued operation as a misfire in a recoil-operated machine gun would, but a jam would most certainly prevent continued operation for some time. Given that a jam might occur when a round is incompletely fed, it is most likely to occur at some point between the maximum reliable speed and the speed at which rounds would not feed at all. $\endgroup$ – Monty Wild Sep 18 '19 at 3:12
  • $\begingroup$ Modern variants on the Gatling are chain-link-belt-fed, and the mechanism pulls the rounds into the receiver as fast as it can rotate... until the forces involved are so high that the links begin to deform. Between gravity-feed and chain-link ammo belts were canvas belts, used by Maxim and Vickers recoil-operated machine guns amongst others, however they tended to stretch when fed too rapidly, limiting the maximum rate of fire. $\endgroup$ – Monty Wild Sep 18 '19 at 3:20
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    $\begingroup$ The best feed system for a Gatling Gun was the Bruce Feed System, which was invented after the Civil War, but doesn't use any technology that wasn't available at the time. Reports of British use indicate, despite occasional jams, that the guns performed well, though this was at a speed of around 600 rounds per minute. Unfortunately, due to lack of literature, I think the only way to determine the best speed would to conduct a test, and I don't own a Gatling Gun. Fair points though - jamming on a battlefield wouldn't be pretty. $\endgroup$ – Halfthawed Sep 18 '19 at 3:56

To prove a Mythbusters related point, scientists at MIT built a steam mortar cannon using technology and designs developed before 200 BC. This mortar could hurl projectiles with more energy than a modern .50 cal machine gun.

As @Separatrix rightly says, steam is an ugly beast that is difficult to fully weaponise. However, the invention of a small and (relatively) portable mortar cannon would allow your army to respond agilely to combat scenarios.

The invention of the mortar (especially one more powerful than a cannon) would allow your Union to lay down cannonfire faster and more frequently than the enemy, so your army's tactics are very difficult to respond to because you could have projectiles flying at the speed of sound at any moment. The stealth advantages of mortars over cannons is also something to consider.

Mortars were reinvented in-promptu at The Siege of Vicksberg in 1863, and proved remarkably effective. In fact, the result was a decisive Union victory that many consider to have been the war's turning point. Any side that developed this technology first (and in a more scientific way than right on the battlefield) would be a serious threat.

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    $\begingroup$ The MIT team is being quite cagey about how their steam cannon works, but it looks to me like a controlled boiler explosion: pour some water into a pipe, jam a projectile in the end, and heat the contraption. If you're lucky, friction between the projectile and the pipe is the weak point, and the projectile goes flying. The big downside is that you can't control when the cannon goes off, you just know that it'll do so a few minutes after it's put into the fire. This is decidedly inferior to existing gunpowder cannon. $\endgroup$ – Mark Sep 16 '19 at 23:14
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    $\begingroup$ @Mark article quotes a time of two minutes to reload and fire. OP simply asks for a good steam-powered weapon- never said it had to be better than a cannon. $\endgroup$ – mcRobusta Sep 17 '19 at 4:32
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    $\begingroup$ @Mark - You could probably get pretty close in predicting the whens, with a fixed amount of water and a decent heat-sense... the same kind of heat-sense people were using to cook over open fires or in wood-fired ovens, where compensating for the variables of the fire is just expected. $\endgroup$ – Megha Sep 22 '19 at 23:44

Building a steam cannon, starting with rank ignorance. Well, a gun is a tube that contains high pressure in it. The pressure accelerates a projectile out the tube.

We have a steam boiler so there is your pressure. It operates over known pressures. How can we manipulate barrel size and projectile weight to make something comparable to existing firearms?

I found this sweet excel table here http://closefocusresearch.com/calculating-barrel-pressure-and-projectile-velocity-gun-systems It does the calculations. I included the whole thing so you can see stats for real guns. Then my cannon.


The pressure from a steam boiler is substantially less than that in a gun barrel. I used 350 psi as representative of boilers from the 1860s. 2 orders of magnitude low. How to fix?

  1. More acceleration time. I made the barrel 10 feet long. The projectile has more time to accelerate. Longer would be better but I worried it might get droopy and people might not think you were enthusiastic for the project. 10 feet is plenty long.

  2. I made the projectile big: 2000 grains. That is 4.5 oz or 1/3 pound - hefty but not stupidly so. Less than triple the .50 cal.

  3. I tripled the bore diameter. Also someone painted it like a barber pole.

The generously long Willk cannon lobs giant bullets at about half the speed of a Minie ball but with the energy of a .44 magnum bullet and a lot of momentum.

The barrel is essentially just a steam whistle: a tube connected to the boiler. For the feed mechanism, a rotating wheel occludes the connection between barrel and boiler, breech slides open, bullet drops in from magazine hopper, breech closes, connection to boiler opens. Repeat. I cannot calculate fire rate. I will assert it is fast but probably not as fast as a Gatlin gun.

A gun like this would be a phenomenal naval weapon for a steamship. You would fire in an arc, as they used machine guns in WW1. The big bullets could travel great distances and would come down through other watercraft or if you were beseiging a city, down through roofs.

Thinking about the steam cannon: bullets would be pointed, hollow iron cups. They would be filled with water then sealed with a cork. They will be lighter to transport & iron is less prone to denting than lead. Water is cheap and heavy and will be used to provide extra mass on site. If water is in short supply, then dirt or rocks.


I think that any civilisation using a steam gun would have to have some sort of inability to produce any other sort of explosive charge that could propel a projectile. Steam although i think would be kind of awesome cannot produce in high enough quantities the required Psi quickly enough to fire a projectile efficiently.

Other types of weapon like maybe a steam powered fist or really anything driven by a piston may well be viable. Steam generally needs time to build pressure.

I guess maybe, water under very high pressure Ie. water forced into a container smaller than water's natural mass perhaps? But then that's not exactly steam, steam being heated water.

I truly wish it were not so.


The fix for the low pressure of the steam piston and subsequent low projectile velocity might be to incorporate it into a 'light gas gun'. In a light gas gun, a large piston is used to pressurize a light gas like hydrogen or helium. This also heats the gas, raising its speed of sound, which gives the projectile higher velocity.

The large steam piston pushes the gas into a much smaller barrel, so the pressures can get insanely high. At the end of a barrel is a burst disk calibrated to blow upen at a specified pressure. When the pressure is reached, the disk ruptures, and all that gas rushes down the barrel at the (very high) speed of sound. This pushes the projectile down the barrel and out.

Light gas guns can attain extremely high speeds. In fact, they are primarily used to test high speed impacts, and projectiles can reach 8.5 km/s - fast enough that if you had one on the Moon, you should shoot projectiles at the Earth. But normally, the super high speed ones have huge pistons driven by explosion, not steam.

Still, a much scaled down, steam powered version of that might still get you some decent projectile velocities.

But I have my doubts that it would ever be small enough that one or two men could handle it, and I certainly wouldn't want to stand beside a steam boiler on a battlefield. It'd have to be incredibly well armored, which would make it not very portable, or it would be a terrific target for the enemy.

More details here: Wikipedia: Light Gas Gun


Not exactly the answer you are looking for, but I would suggest a steam power tank instead of gun. Heavy armor for protection and a early breach loading cannon in a platform moved by a steam traction engine. You could add a couple of Gatling guns for antipersonnel protection.


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