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In the world my friend and I are making, the different races throughout the planet have decided to work on advancing the development of Airgun technology. The main reason for this was that once gunpowder was discovered, it wasn't considered a very safe or practical gun-propellant since the oxygen in the planet was around 33%. Some individuals do still use gunpowder weapons, such as Blunderbusses and Sniper Rifles, but their commonality is seldom, since they are all muzzle and take a while to reload. The only benefit they do provide is Anti-armour and Anti-Megafauna use.

Airfiles on the other hand have a significant amount of benefits, since more time was spent on their development. There are is a wide variation of the gardidoni series, to Volcanics, Revolvers, Bolt-action Rifles; there are even Semi-automatic pistols.

However, despite their wide scope, one significant drawback is low range and power. Since the projectiles are too slow to puncture through armor and gambeson, a new type of ammunition had to be developed.

Instead of metal balls, the Bullets are made of an encasing of glass with a chemical explosive in the center. The idea is that glass itself would only break once it experiences a high force impact; typically subsonic. Once the glass breaks, the explosive is released, creating a high degree of heat so hot it can disintegrate flesh -- also leaving behind bits of glass that can act as shrapnel. Rather then relying on Puncturing the bullets instead rely on shockwaves to disable the target.

The problem that I've been trying to figure out is what substance can these people use as the chemical explosive that make these rounds effective?

An Idea I did think about was the use of fluorine gas. But the problem with that concept is how are they able to store it in the glass? The best idea we got so far was that instead of one chemical substance, there could be two. Perhaps once the bullet breaks, they could mix together and trigger the chemical reaction, but still, how could they put it inside the glass? And what two chemicals can work? I tried thinking about using Hydroquinone and Hydrogen peroxide(What Bombardier beetles use). But even then, I don't think it might produce the desired effect.

Also for specifics. The Muzzle of these weapons are about 11.7mm. While There understanding of alchemy is relatively advanced. The advancement in the technology is around close to renaissance era, with some advancements sprinkled in other areas. I could use a fictional material, but still. Are there real world chemicals we can use as some inspirational basis?

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    $\begingroup$ The impact would break the glass but not detonate the explosive. You would need an impact fuse to trigger the detonation, regardless of whether the outside is made of glass or not. I would wager that this bullet would have little effect anyway because of the tiny charge size detonating against the surface of armor means that most of the blast energy is directed away from the target and what's left reflects off the surface of the armor, much like setting off a firecracker on pavement. $\endgroup$ Oct 8, 2020 at 23:34
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    $\begingroup$ The biggest challenge here is the brittleness of the bullet. If the bullet should break on impact, it would be very hard to avoid cracking when it is fired. $\endgroup$
    – Alexander
    Oct 8, 2020 at 23:35
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    $\begingroup$ Seems like you have invented a bullet with fairly awful characteristics: Low muzzle velocity and inaccurate (glass = no spin) mean close-range use only. Glass means shattering, so limited penetration and potentially defeated by shields or armor. Explosives inside each round means that each round is complicated and expensive and has the potential to blow up in the musketeer's face. But rounds are so small that each won't do much damage. Consider using crossbows (or similar) to deliver a larger, armor-piercing explosive punch. $\endgroup$
    – user535733
    Oct 8, 2020 at 23:50
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    $\begingroup$ What levels of air pressure are your guns operating at? A modern airgun packs enough power to be on par with most conventional firearms and easily penetrates any armor short of kevlar or a plate carrier. Also consider that your airguns could fire flechettes instead of bullets giving them excellent armor penetration capability and requiring thick metal or ceramics to stop $\endgroup$
    – Dragongeek
    Oct 9, 2020 at 3:09
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    $\begingroup$ "once gunpowder was discovered, it wasn't considered a very safe or practical gun-propellant since the oxygen in the planet was around 33%": gunpowder wouldn't behave any differently in 33% O2 atmosphere. Or in 100% O2 atmosphere, or in 0% O2 atmosphere. The whole reason it's useful for propelling bullets is that it carries its own oxidizer and can combust in an enclosed space with essentially no air. $\endgroup$ Oct 14, 2020 at 20:14

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Answers and thoughts on your weapons:

I think you are looking for contact explosives which explode on impact. No glass bullet needed. Just add old-fashioned metal casings (think pineapple-type 'defensive' grenades). A triggering fuse (possible but not developed with advanced alchemy) can guarantee a detonation for the less sensitive types, but otherwise airguns would fire big things (explosives) that would easily go boom on impact (like German stick 'offensive' grenades). Triggered warheads made to work like small shaped charges (think RPG projectiles) would also give you the armor-piercing abilities you crave. Shaped charges are more an application of explosives than a technological limit.

Otherwise consider the introduction of gyrojet ammunitions, which are basically miniature rocket launchers. These are a little too advanced for the period, but small gunpowder rockets could work in a similar way. Airguns would be a good tool to fire these projectiles, which could/would leave the barrel with the rocket igniting after (and you could make them explosive if you like). Possibly the rocket ignites when a string on the gun pulls the inition. The projectile gets faster the farther it goes! I bet you could make a version shedding sparks which would make lines of fire everywhere, if desired.

Otherwise consider sabot rounds firing flechettes to improve armor penetration. I'm assuming your enhanced airguns can match shotguns for velocities. Most munitions for shotguns would work equally well in an advanced version of an airgun. Also multi-stage compression chambers like the V3 weapon to keep increasing velocity.

I can't dispute that there are an endless array of incendiary chemicals that would be fiendish in a high-O2 environment. An airgun (especially a really large-barreled version functionally like a grenade launcher) could fire endless evil. Most chemical weapons, for example, are actually contact compounds, not gasses. A person splattered with phosgene oxime is pretty much out of a fight, and the area splattered with it is unusable to anyone not in a REALLY top-notch hazmat suit. How sophisticated are those alchemists? More primitive toxins and irritants are certainly possible.

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    $\begingroup$ Rockets and explosives (except for fuel-air explosives) are completely unaffected by the oxygen level of the atmosphere they operate in. All of their energy is provided by the chemicals which form them. And contact explosives are always iffy (at best) for projectiles, since they may be detonated by the shock of launching. An airgun and a firearm which produce the same muzzle velocity for the same barrel length will provide about the same setback forces - and airguns are typically worse. $\endgroup$ Oct 14, 2020 at 16:37
  • $\begingroup$ @WhatRoughBeast Fair point about oxidizers, I've updated the answer. I think that in general explosive bullets are a dangerous alternative, especially with lower tech, and fusing is a challenge. That's why I proposed something like contact explosives. Any ideas for something low tech but still explosive that works for projectiles? $\endgroup$
    – DWKraus
    Oct 14, 2020 at 23:06
  • $\begingroup$ Contact explosives are generally categorized as such if they are sensitive enough to detonate at a touch - and you really don't want this for something being fired from a gun (air or otherwise). For that matter, carrying projectiles with a large quantity of contact explosives is a great way to blow yourself up. They are, by definition, touchy. And touchy is bad. You might consider binary explosives, which are kept separate until use and then combined. Some are very sensitive after being mixed, but the issue of a low-tech mixing mechanism is not something I'd care to try. Just assert it. $\endgroup$ Oct 15, 2020 at 16:13
  • $\begingroup$ When I say, "Just assert it." I mean don't pay much attention to it. Present it as a fait accompli and get on with your story. Don't try to describe the mechanism, don't have a character try to build the damn thing while explaining every step. Accept that a few knowledgeable readers will be unsatisfied, but the rest won't know enough to get upset. $\endgroup$ Oct 15, 2020 at 16:16
  • $\begingroup$ I don't think a sabot would translate well to air rifles. Sabot rounds work on the principle of putting more gunpowder behind a slug with a narrower profile. Airguns however want to keep the area between the slug and the air valve as constrained as possible or you just lose power to decompression because the propellant is not actually in the chamber, but another part of the gun entirely. $\endgroup$
    – Nosajimiki
    Dec 23, 2020 at 19:20
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Just for the sake of linking this article, I'd suggest Chlorine Trifluoride, which is an utterly horrible compound from the very depths of some explosive reactive hell. However, I think that it might set the glass on fire, so containing it in glass bullets is probably a no-go.

When it comes to general explosives, the usual formula is cram nitrogens onto the molecule. Nitro groups, nitrates, azides, whatever. Cram them on until you blow up the lab, then make the compound one step down from that first one. These compounds can be ridiculously impact-sensitive, so firing the weapon might be... exciting... but on impact you'd certainly get a large explosion.

Trying out the two-chemicals-one-bullet-route, the first thing that jumps to mind is use pure oxygen and something very very flammable. Pentaborane comes to mind as something ridiculously overpowered for this kind of thing, but really any sort of rocket fuel would probably do.

Other things you could try could be concentrated acids (H2SO4 is always fun when you drop it in the lab), or various more-or-less evil chemical cocktails.

If you want real-world inspiration there's also a concerning amount---perhaps more for irritants than for other uses though. Maybe look at the compounds used in pepper sprays and tear gas, if you're looking for irritants.

Honestly, the biggest barrier here is probably firing the ammunition without breaking it. There are oodles upon oodles of horrifically toxic and/or explosive and/or otherwise nasty chemicals, and when you open it up to mixing two chemicals there are piles and piles of new and exciting exothermic reactions to try.

If you're looking for further inspiration, the Things I Won't Work With category of Derek Lowe's chemistry blog might be a fun place to start.

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    $\begingroup$ Any solution that justifies suggesting it might set the glass on fire gets a +1 from me. $\endgroup$ Oct 9, 2020 at 3:14
  • $\begingroup$ Regarding the fragile bullet problem, maybe en.m.wikipedia.org/wiki/Prince_Rupert%27s_drop $\endgroup$ Oct 9, 2020 at 11:39
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    $\begingroup$ Chlorine Trifluoride is an oxidizer, and won't explode by itself. It would set flesh and blood on fire, though. Along with sand, glas, concrete, water, etc. It has been considered as an oxidizer for rockets, it would deliver exquisite performance burning the fuel. But since it's so hard to stop from also burning the combustion chamber walls, turbo pumps, plumbing, and tanks, it has never seen any use. $\endgroup$ Oct 10, 2020 at 10:40
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    $\begingroup$ +1 for the Things I Won't Work With link. $\endgroup$
    – IT Alex
    Oct 12, 2020 at 17:11
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Chlorine+Brake Fluid

It's relatively easy, although I would suggest against glass for the reason that glass has a likelihood of breaking on the user. The two chemicals that I listed are common, not overly dangerous, and have a strong low-explosive reaction when mixed, without an ignition source. A low explosive might be just what your story needs, since low explosives provide impact and concussion force, while high explosives are generally used to destroy targets.

A plastic lined metal bullet, similar to what are used in modern shotgun cartridges, would work equally well; the thickness of plastic can be varied to allow it to break/compress on impact at subsonic speeds. If glass is important however, the principle is the same. Make two compartments with a thin barrier between them, that will break quicker than the outside cartridge shell, releasing and mixing the chemicals on impact.

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Sounds like an interesting setting! But I would like to raise some points...

First off, explosive rounds like you're suggesting are an incredibly dangerous and unreliable weapon. If they shatter on impact, what happens if you trip and land on your ammo belt?

Second off: What about Poison? We don't poison rounds much because the coating is unlikely to survive the trip, but there isn't much reason not to if the rounds are subsonic and that practically guarantees a kill.

Carrying it around is obviously dangerous but something like lead dust is relatively safe and easy for you to work with proper safety equipment.

Getting the stuff in your lungs or bloodstream though is going to be a bad time to have. Plus the incapacitated soldiers will slow down their buddies as they gradually die.

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  • $\begingroup$ We don't poison rounds because that's prohibited by the Geneva Convention, as well as being utterly useless for military purposes. From a military perspective, a wounded enemy is just as good as a dead enemy. A cynical view would even see the wounded enemy as better because their treatment will drain the enemy of additional manpower. A dead soldier only needs a coffin and a ditch, a wounded soldier may need extended intensive care. (If you ask me, we shouldn't shoot people at all, but alas, my view is not shared among the people with weapons...) $\endgroup$ Oct 10, 2020 at 10:48
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You don't use explosive bullets to overcome armor

You can make explosive bullets quite easily, Sodium/Potassium bullets are a really good example that can be quite devastating against soft tissue... but that is not what you are asking. As you can see in this video, they can make a watermelon explode quite spectacularly, but when it comes to penetration, they have less penetrating power than a normal lead bullet.

If you want to make an explosive penetrate more than a lead bullet, you need to fire a shape-charged bullet such that it is able to explode into an energetic spray with an even smaller radius than your slug, but doing this at the scale of personal firearms is incredibly difficult, expensive, and impractical since such ammo is quite a bit more complex than a simple glass casing. Thus why shape charges are normally reserved for anti-tank weapons.

So, let's look at how the problem of armor is actually addressed in modern warfare. The reason lead does not penetrate armor better is because it deforms so easily on impact. Despite this, harder metals like steel generally do not make for better bullets than lead because they are less dense and do not deform to fill the barrel of you gun when you fire it so it does not impact with as much energy as lead. Since the 1880s, many military grade bullets have been made using metal jackets which were outer coatings of a metal that is harder than lead (typically cupronickel) to improve their penetration. In more recent years, ammunition manufacturers have been using steel tipped bullets. Because the outer layer of these bullets are still lead, they expand to fit barrels very well when fired, but the tip is made out of steel or tungsten which are much harder than lead or cupronickel. This gives these bullets much better armor penetration than previous generations of armor piercing rounds because the tip can maintain its shape better as it pierces through armor while being driven into the target by the dense lead backing.

So, if your civilization were to apply these real world lessons in slug design, you will get a lot of the same results.

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Glass would make a terrible projectile, as it is far too low in density to be spin stabilized by rifling, and even if stabilized it would still shed velocity very rapidly. The range would be very short and the impact energy quite low, and accuracy exceedingly poor. Iron (steel) is about the lowest density material to make a practical bullet out of and any explosive filler would have more than enough power to fragment the case of the round on impact - it doesn't need to break on impact.

The high oxygen atmosphere does open up the possibility of making the guns themselves operate on a diesel cycle, where a piston compresses the air and a fuel is injected into the hot compressed air and greatly amplifies the power as it explodes. A more elegant design would simply pack wax into the base of the bullet, and the high pressure and hot high-oxygen compressed air would vaporize and ignite it, working much like gunpowder but without the hazards. Bonus points for making the piston lock in position on ignition so it doesn't rebound and waste gas pressure.

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