How would projectiles used in my magic gun look like?

Question

So, advanced [on average comparable to the end of 19th century Europe/America, though diverging in specifics due to magic] magical civilization has a problem. They have unique magic guns, that work on a principle where magic is used to accelerate any solid projectiles inside[well, any solid projectiles except for metals, as explained later]. Magic propagates slightly slower than 500 m/s, making that the top speed of projectile fired by such weapons.

But magic and metals don't work well together. While non-reactive metals (Gold, Platinum, Silver, Copper) can be used to reflect magic, all the metals are unaffected by direct magic manipulation and reactive metals have an even distributive effect on magic within a few centimetres around them, so you don't really want to make metal bullets, because those wouldn't work.

Luckily, at least in the form of compounds (such as oxides, sulphides, etc.) of metals don't have this annoying problem for magic guns, the problem only manifests if the structure of metals is present, so at least in that way, there are multiple possible materials to use.

Things I think need to be taken into account:

• Unlike with explosive firearms, magic firearms don't need propellant.
• The magic gun continuously delivers force and creates something like an acceleration field inside the barrel, so it's far easier to accelerate long ammunition than with conventional gunpowder-powered ammunition (since the force that ammo is subjected to grows at almost the same rate as mass of the ammo does).
• How would one make this ammunition work with rifling?

So, with these restrictions, what will ammunition for handguns, long guns and cannons look like?

Answer 1

Material choice for your bullet seems likely to devolve to glass, stone of some kind, wood, or various minerals -- most of which are compounds of metals, but the question says compounds aren't a problem, only the pure(ish) metallic material itself.

However, most of these material choices aren't likely to take rifling, and it's obvious the barrel can't be made of a material like steel, so the projectile will have to be aerodynamically stable, like an arrow.

To me, in a context of guns, that says "flechette". The name is derived from French for "arrow" with a suffix indicting it's small, and that's pretty precisely what they are. When made for modern firearms, they're manufactured rather like common wire nails, with the heads deformed into a set of vanes (like feathers on an arrow, or the vanes on a dart).

In early examples, they're likely to strongly resemble an actual dart (that you'd see stuck in a bristle board in a pub), with a wood shaft, stone point (since it can't be metal), and actual feathers. Later, it'll be miniaturized and molded from tempered glass, machined from some homogeneous stone, or even grown as a single crystal like a laser ruby.

At only 500 m/s they'd lack the punch of a modern bullet, but they'd make up for it (especially if grown in corundum) in penetration -- a shaft a few millimeters in diameter, and twenty times as long as it is wide, will have the sectional density to both hold its velocity well in flight, and penetrate even pretty good (magic-proof, because steel) armor. And at that size, it'll put down an enemy about as effectively as a First World War rifle bullet.

Answer 2

Glass, Concrete, and Explosives

Ammunition could look any number of ways depending on the rules of your magic and universe. Sticking with more of a "replacement" for our world's ammo to be used in your magic universe, ammo could be roughly the same and shape, or simple spheres. These could be manufactured as glass, as concrete, or some type of container for explosives.

Glass is made from sand (grossly oversimplifying). Glass is relatively easy to mold and mass manufacture, is resistant to a wide range of temperatures and conditions (especially soda-lime glass), and is incredibly strong. Magazines could be the same (simple plastic spring-loader to auto-load the ammo into the chamber).

Concrete/cement is also easy enough to manufacture, with even the Romans making it from lime and volcanic ash. It would not be as easy to make small ammo with concrete/cement, but you could certainly make long-range weapons from it (such as the huge shells used in war ships).

Explosives can be made from various materials and liquids. Not wanting to give anyone any ideas, I'll just say that simple potassium nitrate contained inside of a glass, fiber, or wooden casing could be explosive on impact. Kinda like a mini pipe-bomb. Anything that takes significant impact to spark or detonate would work as an explosive inside a shell.

Answer 3

Metals are fine. From my understanding of the problem, the bullet itself being magical is not important, only that the bullet exits the weapon with sufficient lethality.

If the magic field does not affect the motion of metal objects, I would use a sabot (https://en.wikipedia.org/wiki/Sabot_(firearms)) of whatever magic-susceptible material you choose, enclosing a inert/reflective metal bullet (most likely copper). Diffusive metals still fail, for obvious reasons. The advantage here is that the part you are using to react with the magic field is not required to be intact after the bullet leaves the barrel, and the part that has to handle travel and impact has fewer magical constraints.

If using a needle-like projectile, there will be little to no overlap between the projectile and casing cross-sections, minimizing reflection concerns if the magic field is generated at either end of the weapon. I would need to know more about the details of the reflection to comment on how a field generated by the barrel (i.e. the magic itself is moving inwards) would be affected by this setup. More standard-shaped bullets could be fired if you can ensure the field behind the projectile is fully absorbed by the sabot before reaching the reflective area, though the needle style has more penetration for the same mass.

Of course, if having noticeable amounts of metal inverts the entire field, just build the gun backwards. Similarly, if magic does accelerate metals, but in a nonstandard direction, this can be accounted for and an all-metal bullet can be used.

Sorry, metal/magic incompatibility is a major pet peeve of mine and I feel the need to work around it.

Answer 4

More interesting might be the firing mechanism rather than the bullets.

For the bullets you "simply" want hard materials for armor penetration. For non-armor purposes you can use less hard materials like the already mentioned types of glass, plastics or other compounds. Certain sillicon oxydes would fit the bill for example. Their shape would largely be the same. Its shape is designed mostly for getting to the target and doing something to it and less for being fired.

Firing is interesting here. Our current projectiles require pressure to be fired and as such making the bullet and barrel fit as neatly as possible is important to make sure no pressure is lost during firing. But your bullets dont need any of that, as long as they can exit the barrel without slamming into the sides they are golden!

For this reason a few things need to be known: can the direction of the field be changed on the fly, how hard can it push (does a pistol bullet already reach 500m/s before exiting the barrel?) and can the fields be created in layers?

If they cant do either of the above: the bullet will sit in a chamber where the sides of the housing keep it in place. The top of the field moves right, the bottom moves left (but only when the safety is off). This spins up the bullet before it enters the barrel. When fired the bullet is pushed forwards while whatever anchors it so it doesnt fall out moves away. This pushes the bullet into the acceleration field and out the barrel.

If the directions can be changed or you can have layers it can get interesting. The bullet is levitated all the way, hanging inbetween fields of forces that push it back to the center. You'll be unlikely to ever move the gun fast enough to dislodge it. In the center the bullet is spun up (even better if the bullet is hollow and has an internal core spinning around an axis) to give it the stability normally provided by rifling. Upon firing the fields are altered to push it down the "barrel", which could even be partially open, square or whatever. This bullet would move relatively straight if its a normally shaped bullet and the spin can be kept at similar speeds rifling gives it to prevent too much spin drift. In the case of a housing around the spun up bullet you lose the spin drift (I think) and use the extra spin to drill through the target.

But what about using a kind of flywheel? Your magazine becomes a thin circle that is inserted in the "gun". Just imagine this gun but wih the circle off-center or the circle being vertical instead of horizontal: https://images.app.goo.gl/4eVBSd5cQqCuE66b9

The magic spins up the circle around its center, meaning the bullets themselves which are farther from the center spin faster (and could be far enough away not to interfere with magic if they were metal). The gun "fires" simply by using a mechanism to detatch bullets as they pass the barrel and their tangential speed would take them straight out. I think it would have a positive effect in recoil as well but I'm not sure. It would mean it becomes harder to turn your weapon though, so maybe you only spin up the weapon when you are ready to fire? An advantage might be the ability to take the flywheel out and attach virtually anything bulletshaped. So in a pinch soldiers could use presses to press some kind of material they found in a bulletshape and put that in the flywheel.

Answer 5

Several answers here have provided apt suggestions, here are a few ones I could think of :

• Wax/Clay : this may sound surprising, but soft wax/clay bullets, while obviously non-lethal, could provide a range of possibilities. Most of all, they could be filled with poison ; as the gun works with seemingly progressive acceleration, the bullet would not break upon firing, but instead penetrate its (fleshy) target and spread the poison within. Glass can also be used for that purpose, but glass has the distinct disadvantages of being more expensive, taking longer to fabricate, and to be much more fragile and thus not adapted to battlefield conditions (especially regarding safe storage).

• Stone : fairly obvious and self-explanatory. Before being made of cast iron projectiles were made of stone. Stone is readily available everywhere and more than enough to deal with infantry. Fortresses or other tougher structures will most likely ignore the damage dealt by stone projectiles (if correctly built).

• Inflamable liquids : the guns could instead be made into sprayers, and spew liquids that are ignited at the end of the barrel to function as flamethrowers (much like the Byzantines' syphons).