If humans had no access to gunpowder, what else would they use to power guns?

Question

In my setting there's a lack of sulfur, simply put. Don't ask for the specifications, just assume that whatever amount there is, it is likely better off used in dietary supplements for the shortage of it.

Without access to this, what other propellants would humans use?

If possible, I'd like to know how effective those would be compared to gunpowder.

Edit for context: I am most concerned about the pre-industrial period. I appreciate those telling me about railguns and superheated water, but you need to walk before you can run and I want to figure out what everyone's doing for the 500-700 years before contemporary science makes those plausible.

Answer 1

Gunpowder with a different ignitor than sulfur.

A primer on explosives for coal miners. US Geological Survey Bulletin 1911

The heavy lifting in gunpowder is done by charcoal (the fuel) and potassium nitrate (the oxidant). Sulfur is in there because it is easily ignited, and it then ignites the charcoal.

In your sulfur deficient world people use different accelerants. Distilled alcohol is a common one, and alcohol in this role is sometimes doped with turpentine. Long term gunpowder storage is in glass bottles or tarred kegs. For cannons, glass bottles of gunpowder in alcohol are broken into the cannon or hole before wadding and ball, or powder is scooped out of the keg and used as a wet paste. For rifles the gunpowder is parcelled out before expected use into waxed paper envelopes. The alcohol evaporates from these over a week or two.

I am very pleased this question led me to find the primer on explosives for coal miners linked above. I love the way they wrote in 1911.

Answer 2

I present you a real weapon used in real wars, made in 1779.

The Girardoni air rifle.

It was not merely an experimental curiosity, it was mass-produced and was in active military service for decades. It had a much higher rate of fire than muskets, and although less powerful, it was still lethal at the ranges typical musket engagements were fought at.

The downsides were that it was much more maintenance-heavy and expensive, so they went back to traditional gunpowder after a few decades of use, because it was much more practical to have cheaper guns any soldier could repair in the field, than having delicate and complex weapons which required specialized training to maintain.

But with gunpowder lacking completely or in extremely short supply, I can't see any reason against a more widespread adoption of these guns.

Answer 3

Steam or compressed air come immediately to mind.

It doesn't take long to figure out that a heated container with water inside will end up exploding. It might not be as handy as black powder, so it might not out-compete bows until other explosives are discovered or compressed air is made available.

Answer 4

As Willk notes, it's apparently possible to make working gunpowder without sulfur, it's just hard to ignite.

However, if your civilization really has no access to gunpowder at all (maybe due to lack of usable sources of saltpeter?), they could just jump straight to what was historically the next step in gun propellants in our world: guncotton (nitrocellulose).

Making guncotton basically just requires some way to produce concentrated nitric acid — which of course might be a problem if your world is poor in nitrates such as saltpeter. But there are several different ways of producing nitric acid (the modern process starts with ammonia, but you can also make it literally from thin air) and it's at least conceivable that, without easily mineable saltpeter deposits, your civilization might stumble upon a practical way to make and concentrate nitric acid before figuring out gunpowder.

Of course you can make saltpeter from nitric acid, once you have it, by reacting it with some source of potassium. But once you have nitric acid, you might well discover guncotton before gunpowder.

In particular, once you have nitric acid and some brave chemists playing with it, the discovery of guncotton seems all but inevitable. To quote the Wikipedia article I linked above:

Around 1846 Christian Friedrich Schönbein, a German-Swiss chemist, discovered a more practical formulation. As he was working in the kitchen of his home in Basel, he spilled a mixture of nitric acid (HNO₃) and sulfuric acid (H₂SO₄) on the kitchen table. He reached for the nearest cloth, a cotton apron, and wiped it up. He hung the apron on the stove door to dry, and as soon as it was dry, a flash occurred as the apron ignited. His preparation method was the first to be widely used. The method was to immerse one part of fine cotton in 15 parts of an equal blend of sulfuric acid and nitric acid. After two minutes, the cotton was removed and washed in cold water to set the esterification level and to remove all acid residue. The cotton was then slowly dried at a temperature below 40 °C (104 °F). Schönbein collaborated with the Frankfurt professor Rudolf Christian Böttger, who had discovered the process independently in the same year.

By coincidence, a third chemist, the Brunswick professor F. J. Otto had also produced guncotton in 1846 and was the first to publish the process, much to the disappointment of Schönbein and Böttger.

Note the independent (and at least partly accidental) discovery by three chemists at almost the same time! This strongly implies that it was very much a case of it being "steam engine time", with the conditions simply being right for the discovery to be made by someone experimenting with the available chemicals, rather than the discovery itself being the chance result of some particularly uncommon luck or effort.

Of course, after guncotton was discovered, there was still a considerable amount of further innovation and refinement to be done to deal with issues such as storage stability and to produce improved types of "smokeless powder" such as ballistite (a combination of nitroglycerine, and guncotton) and cordite (nitroglycerine, guncotton, petroleum jelly and later nitroguanidine). But that's not fundamentally different from the gradual refinements and improvements made to gunpowder after its discovery too.

Answer 5

It is possible that firearms aren't even used. Gunpowder has historically been fairly easy to produce and manufacture at scale, and while other responses such as coilguns, steam, and railguns are interesting to consider, they are often highly complex and fairly difficult to manufacture at scale, especially for an evolving economy or society. Coilguns and railguns in particular require rare earth materials that are unlikely to be found without advanced drilling and mining techniques, but historically mining was often done with - you guessed it - gunpowder.

In my opinion, it's likely that the primary source of weaponry in a sulfur-less environment would take the form of rockets - rocket propellants, such as ammonium/potassium compounds plus aluminum and oxides, are considerably more plentiful than REMs and their launch mechanisms involve fewer moving parts than many other forms of weaponry. Liquid propellants, such as nitric acid (TNT, which doesn't involve sulfur), and hydrogen peroxide, are also fairly inexpensive to produce relative to the amount of damage they can cause.

In my opinion the most likely scenario is a compressing of rockets into small explosive shells that can be fired from a device roughly the size of a rifle or a handgun. Such a device would probably be little better than an 18th-century musket, but consistent evolution in this field would likely enable the miniaturization of these devices and increased rate of fire and reload time.

Answer 6

They might stick with bows and crossbows a lot longer

Black powder weapon advantages

There are basically two advantages to early gunpowder-based weapons, that both turned out to be quite useful in early modern Europe, and led to further development:

Siege weapons

Early modern Europe had mostly small armies, and lots of castles with tall but relatively thin walls that were easy to defend with small garrisons. These are almost uniquely vulnerable to early cannon. It took some time to develop cannon to the point where they could rapidly and reliably batter down those walls, but once that was achieved, walls suddenly turned out to be almost useless. (this didn't apply in china, as they mostly used much thicker walls, filled with earth)

This led to the development of fortifications with thicker, lower walls, but those couldn't rely on the difficulty of scaling them, so you instead needed a large garrison that could effectively threaten attackers. That leads us to the second advantage:

Guns are easy (relatively speaking)

That's not to say that a gun is trivial to make, to make ammunition for, or to operate, but it is much faster and easier to train a peasant to use a gun than it is to train him to use a (war)bow. So if you suddenly find yourself in a situation where you need to massively expand your army, and arm them with ranged weapons (spears are cheap and easy, but they won't help you much when defending a star fort), in order to defend your fortifications, they're the best option you have. This was very much the case in early modern Europe.

So what happens without black powder?

Later guns

Well, if the industrial revolution happens, as Ilmari Karonen says, eventually nitric acid will lead to the development of guncotton and other suitable explosives. That will almost inevitably lead to guns. Earlier, the development of pressure vessels might give you airguns, but until either of those are compelling enough to force a switch, armies might continue to use and further refine bows and crossbows.

State formation

Gunpowder-based warfare was very important to the political history of Europe. Without it, the nation-states that you know might not exist, which all sorts of knock-on effects.

The industrial revolution

For instance, the industrial revolution might not have happened there, or at all. In Britain, it required large coal deposits, the depletion of forests (for firewood and charcoal), the existing knowledge of early pressure vessels (from black powder weapons), all contained in a large state doing lots of trade (so greatly increasing production of, well, anything, wouldn't crater prices), allowing early "burn coal to power a very inefficient pump to drain the coal mine so you can dig up more coal" engines to be developed and adapted to power factories.

Answer 7

Coilguns

Actually, it depends on how advanced these beings are. Assuming a level of advancement below or only barely that of modern humans, I would go for the compressed-air device suggested by L. Dutch above. However, as technology advances, there may be a better option.

Meet the coilgun: this bad boy works by using magnetic forces to accelerate a projectile to supersonic speeds. Effective? Uh, did I say supersonic? This device is basically a handheld mass driver. Okay, so we don’t quite have these puppies yet, but hey, maybe your civilisation is farther ahead than us, tech-wise.

Answer 8

Mechanical Tension/Compression weapons

Prior to the advent of firearms, their nearest equivalent was probably the Crossbow and its bigger cousin, the Ballista.

Take a strip of bendy metal or wood, pull back the end via cords and possibly a winch.
Basically an adaptation of the slingshot for enhanced power and accuracy.
A well-made crossbow could put a metal bolt straight through the best body armour of the time at any range you could reasonably expect to hit at.
More than sufficient as a weapon of war, and substantially easier to train with than the Longbow it competed with. It made ranged combat something that could be done by minimally trained Militia and Helots rather than life-long professional bowmen.

You might also explore the Discworld concept of the Spring-Gonne. A spring-powered compact crossbow.
This concept may also be found in Frank Herbert's Dune in the form of the Maula Pistol. A spring-powered dart-gun loaded with poison darts.

Springs tend to pack a lot less force than a crossbow, in large part due to inefficiencies in the spring and challenges in manufacture, but they're excellent options with light projectiles.

Answer 9

In the context of your setting, guns just wouldn't be used before the industrial age, where mass-producible alternatives to gun-powder would by readily available.

People would stick with alternatives, such as repeating crossbows ---the real-world chinese army used those until 17-hundred-and-then-some.

Answer 10

If humans had no access to gunpowder, they would likely use alternative forms of propulsion for firearms, such as:

1. Springs or compressed air
2. Nitrogen-powered combustion
3. Pneumatic or hydraulic pressure
4. Electrical or magnetic systems
5. Rocket propulsion

These alternatives would provide the necessary energy to propel a projectile out of the barrel of a firearm.

Answer 11

Ye Old Elastic Materials

Since before the first gun, humans have used the principles of elasticity to fling sharpened sticks or small-to-medium stones at each other or at animals they wish to send back to their respective culture's creator.

Slingshots and Bows should suffice and don't use any chemical or electrical propellents, the ammo is even reusable, mostly.

Bows take more skill and strength to use, but you can train any old peasant to use a crossbow and children can learn how to fling a rick with a slingshot, plus the projectile is slow

Answer 12

The Sims-Dudley Dynamite Gun was tested in the Spanish American War:

https://www.spanamwar.com/dynamite

With a different source of compressed air (it used a small black powder charge to throw shells) something like the Dynamite Gun might work for you.

If your world has lots of electricity to spare, consider calcium carbide:

https://en.wikipedia.org/wiki/Calcium_carbide

... which produces acetylene when wetted, delivering a pretty good bang:

https://en.wikipedia.org/wiki/Bamboo_cannon

Answer 13

There are plenty of air rifles available now, which, with a little tinkering, can produce pressures high enough to make them deadly to humans. They're only usually under-powered because of government regulation (speaking of the UK here). You could quite easily produce a deadly airgun. It's just a bit of plumbing and a bit of clockwork.

Before that, we used tension. Bows and arrows, and catapults. Crossbows were particularly deadly, armour-piercing even. To tension them ready for firing often took the strength of the soldier's whole body, putting their foot in a loop at the bottom and using a strong lever to pull the string back. The energy was stored in the springy steel.

EDIT: Browsing about steam-powered guns, https://en.wikipedia.org/wiki/Steam_cannon there were a few. Not great successes but if there'd been no gunpowder, perhaps they'd have put more work into developing them.

Answer 14

Strong rubber bands (i.e. slingshots, or sling bows) could be a viable alternative, specifically if used in combination with some kind of device that allows tensioning them while investing less muscle power.

This guy might give you some ideas:
Joerg Sprave - @Slingshotchannel - YouTube