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I am currently making a science fiction universe set in a very distant future. Someone suggested that the weapons should use caseless ammunition. However, I cannot find a reason to why you should adopt them as they are usually more sensitive to the environment, are more fragile and have poor sealing - problems that the H&K G11 fought with and which are general problems with caseless Ammo. Some of them are discussed in this NDIA talk.

What kind of materials should be used to at least overcome the rough handling issue? The sealing problem could be solved with a rubber ring like the French chassepot.

I thought of using a similar material to those used in combustible casings used in some tank shells to surround the propellant, however I don't know whether or not this is practical, and if that still counts as caseless if the propellant is surrounded by a combustible "liner".

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  • $\begingroup$ Obturation isn't the problem it was a century and a half ago. Naval ship rifles are caseless (at least those bigger than 5 inch bore), and obturate well. Making propellant that stands up to rough handling and still burns instantly is well nigh impossible. $\endgroup$
    – Zeiss Ikon
    Aug 6 '21 at 13:55
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    $\begingroup$ have you looked at the modern caseless ammunition, like the one used in current LSAT military trails or the Voere VEC-91. $\endgroup$
    – John
    Aug 6 '21 at 14:31
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    $\begingroup$ All of the issues that you list are engineering/science problems, not fundamental issues with the concept. The reason caseless ammo has issues like poor sealing, fragility, bad environment resistance, etc, aren't because there's something wrong with caseless ammo, it's simply because our scientists and engineers simply aren't good enough to figure it out yet. Attempting to predict the future is generally...not a good idea, but I'd be willing to bet that our materials science technology will be advanced enough to get rid of all these problems within half a century at most. $\endgroup$
    – Dragongeek
    Aug 6 '21 at 17:06
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    $\begingroup$ Continued: that doesn't mean caseless ammo as a concept doesn't have fundamental problems though--notably the lack of brass shells which carry heat away from the receiver in a normal gun. In a caseless weapon, all that excess heat needs to be managed somehow, which means you need a gun designed to handle it. $\endgroup$
    – Dragongeek
    Aug 6 '21 at 17:09
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    $\begingroup$ Gyrojet had other problems -- poor accuracy (because it was still accelerating for 6-8 meters after leaving the barrel, and due to the slow barrel time by gun standards), difficulty clearing a misfire, and perceived (true or not) poor durability of the extremely lightweight launcher -- they've been reported as feeling like a toy in the hand. And any gun will function in space, as long as the steel parts are kept warm enough or previously cryo treated. $\endgroup$
    – Zeiss Ikon
    Aug 8 '21 at 0:40
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You're treating the distant future as if it's today...

Demanding that the future comply with today's technology does not a good story make. Let's flip the perspective so you can see the problem: can you imagine talking to someone in 1799 about cased ammunition? Oh, people might appreciate what it could do... but the idea of having it would be laughed at.

Utterly ignoring every conceivable weapon that exists today (because not a single one of them will exist in the distant future other than as antiques), what problems are we trying to solve and how might those solutions be manifest?

Cases:

  • are heavy,
  • limit the number of shots,
  • solve some engineering problems with the barrel, but that can be fixed at the barrel
  • depend on an uncompressible powder,
  • can, themselves, corrode,
  • depend on complex loading mechanisms...

How would I improve on all that?

With a fluid

Explaining how this fluid would meet all the causes-a-big-bang expectations currently filled by gunpowder is irrelevant.[1], [2] After all, it's the distant future where those problems have been solved (unless it's the rare case of narrative necessity, but that should cause you to ask, "is that level of detail really necessary?")

But I love the idea of a fluid. Two fluids, actually, both highly compressed. One, when injected into the weapon, resolves into a solid projectile. The other, when injected into the weapon, resolves into an immensely combustible gas. Bang! Cry of pain, cut to black.

The barrel is frictionless, reducing heat. The injection of the bullet material fills all the available space like expanding foam. (How do you get the point? You're worried about too much detail! :-) ) Residue, if there is any (distant future...) can be ejected with a quick burst of air drawn in with a compressor from the outside world.

Whether or not there would be caseless shells is almost a question of aesthetics

It's your world, so you can use any rule you want. There is no "as real as possible" when it comes to the distant future. We used caseless shells in the past. We use caseless shells today. I think it's more than believable that we'd use caseless shells in the future. But there is one thing you've gotta do...

Stop trying to make your distant future compliant with today. Otherwise, what you have is today.

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  • $\begingroup$ I never tought of doing that. Thanks. $\endgroup$ Aug 6 '21 at 14:28
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    $\begingroup$ You're welcome. However, as much as I love getting those green checkmarks, we do recommend that you hold off selecting a best answer for at least 24 hours. We have amazing users all over the world who could give you a better answer and human nature is to ignore questions that have already been answered. $\endgroup$ Aug 6 '21 at 14:35
  • $\begingroup$ An even more future tech variation of this I once saw was in a book called Old Man's War. Alien threats were so diverse, they needed a ubiquitous weapon that could deal with all of them. So, their guns themselves were more or less a fluid (nanobots) and contained a reserve of fuel and extra nanobot fluid which it could use for arbitrary purposes. This way the gun could shape itself into a low caliber assault riffle, a high caliber sniper riffle, a rocket launcher, a flame thrower, a laser gun... basically whatever form the user needs at the time, the gun could take on. $\endgroup$
    – Nosajimiki
    Aug 6 '21 at 17:52
  • $\begingroup$ While you don't need to go quite this high tech, it does bring up the argument that once you make your ammo fluid until fired, you are no longer married so much to specific slug types or mussel velocities based on what you load the thing with. $\endgroup$
    – Nosajimiki
    Aug 6 '21 at 17:54
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    $\begingroup$ @JBH now I have to ask this on the physics site. $\endgroup$
    – John
    Aug 8 '21 at 2:59
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Don't Use Chemical Propellants

The advantages there are to using a case are numerous. The small amount of extra weight you get from the case does more than just give you a place to put your propellant; it helps with bullet alignment, sealing, heat dissipation, etc. The big issue with caseless guns is that they are so similar to firing bullets that it is hard to get much benefit out of removing the case because improvements that make caseless better will generally also be able to be applied to making bullet firing guns work better. So it is very likely that bullets will always be preferable.

So, to get around this, you need a weapon that functions differently than a ballistic gun, but has the potential to outperform bullets in key metrics using innovations that do not directly help bullets get better.

The Solution: Rail Guns

When we look at railguns, we have the potential for a viable weapon system that fires a slug without getting any benefit whatsoever from a case. Large railguns like those being mounted on some modern naval ships have certain advantages over traditional ballistics including a lower cost per shot, and a much higher mussel velocity which gives it a better effective range and armor pentation. A railgun has a higher theoretically possible mussel velocity than a gun because of how it accelerates the shot. A gun exerts a lot of heat and force on the gun in the chamber and these forces quickly fall off as the slug enters the barrel. A railgun however is accelerated evenly across the whole barrel; so, there is no one major stress point or part of the mechanism being superheated to its melting point.

All this said, railguns are heavier than ballistic cannons of similar fire power and with modern technology we do not yet have the ability to miniaturize them into a practical weapon system due to power limitations and weight constraints. Another reason we don't see hand held railguns is that modern firearms already have such a good range and armor penetration that even if you could miniaturize the advantages of a rail gun, the benefits would all be wasted on a fight between human combatants... however, due to the current direction military technology is going in, this fact may not hold for very many more years. Some of the recent/near-future advances I am talking about include:

Better Ballistic Armor: Over the past few decades, improvements in material science have reduced the weight of personal body armor compared to its protective quality about 5 fold! So bullets that used to require 20mm armor can now be stopped by newer armors that weigh as much as 4mm of the older model armor. This has caused arms manufacturers to step up their game with things like saboted and tungsten tipped bullets but it is currently estimated that many materials we make today could be improved another 5 fold as we continue to approach perfect crystalline materials. So, eventually body armor may just get to tough for our slow, chemically propelled bullets to pernitrate.

Exoskeletal Suits: These suits can increase a soldier's carry capacity to several hundred pounds allowing him to carry enough armor to stop pretty much any caliber of modern anti-personnel weapon. Sure you could also scale up your guns to hand-held 20mm autocannons, but ammo costs go up pretty quickly as you make the bullet larger whereas an equally penetrative rail gun sabot could be nothing more than a 10mm tungsten tipped steel rod launched using an amount of electricity that can be measured in cents instead of >100\$ like many modern high caliber AP rounds.

Self Aiming Guns: A few years back someone invented a hunting riffle that used image recognition and environmental sensors to make a self-aim-correcting riffle. With such a weapon, even an untrained shooter can hit targets over 1km away. So, as AI assisted aiming moves into the realm of military use, having mechanically more accurate/highspeed weapons could become important. Even if you are only engaging a target at 100m, a higher mussel velocity could make the difference between an AI being able to predict the target's body position far enough into the future to be able to either put a bullet through someone's eye or glance off the side of their helmet if they make an unexpected movement at the last minute.

Robots: Then there is the combination of all of these technologies which are semi-autonomous robotic combatants like the IDF Jaguar which does not even have a human inside. Not only do these bots have all the advantages I've mentioned so far, but they also have a LOT more internal room to spare than human infantry for carrying the power systems required to host a rail gun.

So, as these technologies mature and warfare replaces human infantry with AI supplemented mini-tanks, chemical propellants may just not be up to the job of future warfare making caseless firearms in the form of railguns the new standard.

What about the "very distant future"

Everything so far answers this question in regards to the near future where science and military technology can be extrapolated based on what is true today, but as JBH's answer points out: the distant future is unknown ... but we may still be able to make some good guesses about it...

One thing I would guess about it is that we're probably not even throwing kinetic projectiles at each other anymore. The most likely weapon class to evolve into a ubiquitous future weapon system is more likely going to be some variation of the High Energy Laser. Kinetic penetrators of any kind just move so slow that an adequately advanced system would have the ability to see it coming and deploy a countermeasure in its path whereas lightspeed weapons arrive at the target at the exact moment you become able to detect its path. This means that at least some energy will always reach you before you can obstruct its path.

Some laser configurations like that studied at the National Ignition Facility in California can heat a material up enough to trigger a fusion reaction in just a few picoseconds; so, we can assume that it is at least conceivable that future beam weapons will do the same. So not only do you get hit at the exact moment your countermeasure systems see it coming, but by the time your AI can process that it is being hit, you've already absorbed enough energy to turn a small area of your surface into a tiny nuclear explosion.

To put this into perspective: think of guns as the modern equivalent of classical era melee weapons (swords, spears, axes...), and lasers are like classical era missile weapons (slings, bows, pilia...). 2000 years ago, both melee and missile weapons had their place on the battlefield, but by in large, it was the melee weapons that really carried armies to victory. Overtime, everything improved: mild steel short swords evolved into spring steel longswords, and bows evolved into muskets. But as things improved, the limitations inherent in melee weapons became more and more pronounced until the very idea of these melee weapons as a primary battlefield weapon disappeared. Likewise, the problems inherent in slower than light weapons will only get worse as time goes on until the absolute most advanced possible kinetic projectiles achievable will be considered about as useful on a far future battlefield as a pike block is today.

To be clear, I'm not saying that far future weapons will actually be lasers. They may not even be electromagnetic in nature. Just like a bow is not an assault riffle and an arrow is not really a bullet. But what I am saying is that distant future weapons will have a lot more in common with a laser than a gun.

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I've studied this in detail about a decade back, for a high-realism, near-future scenario. The best answer I've arrived at was:

Electrothermal ignition.

In essence, use a low-power version of https://en.wikipedia.org/wiki/Electrothermal-chemical_technology.

Cook-off occurs because the propellant has to be easy to ignite with a chemical primer. With electrothermal ignition, the igniting jet delivers both high heat (3000K+) and pressure, allowing highly insensitive propellants to be used. It can also ignite a large surface area of propellant all at once, not just a single point.

Insensitive propellants solve the cook-off issue. The rest can be handled through less-common, but already currently available materials. The chamber may have to use exotic alloys or CMC. Do not use any sort of rubber, the gun will get hot.

Highly insensitive propellants can also use a larger proportion of plasticizer, making them durable enough for a well-manufactured weapon with tight tolerances. Dirt resistance for a caseless weapon will be necessarily reduced compared to what some cased designs (the AK family) can get away with, but it can still be good enough.

Electrothermal ignition requires the weapon to use a power supply. Power can be recovered from propellant gases, to some extent, but this is complicated. The most realistic scenario is that caseless ammunition guns will require batteries.

For big guns, power is already a given in almost all cases. A modern carbine fitted out with "tactical" gear will already have multiple batteries. In a more distant future, a central battery and a power distribution rail (likely embedded within the same Picatinny system) can be expected.

Whether it's a magazine-embedded disposable battery or an internal rechargeable battery is up to you as the writer.

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The primary advantages of caseless ammunition are lower weight per round, lower cost to manufacture (due to no extensive forming operations to make metallic cases), and no ejected cases to potentially cause problems with nearby people or machines.

The disadvantages are fragility and vulnerability to environmental moisture, heat and cold.

For an application, like self defense or military operations, where reliability is the number one concern, followed by storability and accuracy, it's unlikely that caseless will replace metallic (or partially metallic) cases resembling modern conventional ammunition. The case does such a fine job of protecting the primer, propellant, and bullet, while positioning them for accuracy, that all the evolution of in-service small arms ammunition over the past century and a half (as of 2021) has led up to what we have now: brass, steel, aluminum, or metal-and-plastic cased ammunition.

Another advantage of a fully metallic case is that it carries away a significant fraction of the heat generated by propellant combustion -- heat that can only be absorbed and conducted away by the chamber, barrel, and receiver in a caseless firearm. During rapid fire (as with light or heavy machine guns, submachine guns, and some assault rifles) this can become very important, as excessive heating of the gun's metal parts can affect accuracy, injure the user, or lead to "cook-off" in which a round chambered after a rapid fire situation goes off uncommanded simply due to heat (yes, case ammunition can still do this, but it takes more firing to heat the gun to this point).

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  • $\begingroup$ there was a caseless ammunition rifle in the LSAT trails, weight and not having an opening for dirt to get into the rifle were the big advantages, heat was the biggest problem. a case joes nothing for accuracy. $\endgroup$
    – John
    Aug 6 '21 at 14:34
  • $\begingroup$ @John Don't tell the guys who spend time lovingly ensuring all their cases are identical that it does nothing for accuracy. It can be the difference between military/hunting accuracy and one-hole groups -- but doesn't have much if any effect on "good enough". $\endgroup$
    – Zeiss Ikon
    Aug 6 '21 at 14:38
  • $\begingroup$ that is consistency which is true of anything, it is not something inherent to cases, that is like saying gasoline cars are better because they have power steering, the latter is not dependent on the former. $\endgroup$
    – John
    Aug 6 '21 at 14:42
  • $\begingroup$ @John, A case gives a longer contact surface for holding the slug in alignment. The difference this makes may be negligible for most practical purposes, but they are not completely unrelated factors. It's like this: imagine holding a laser pointer between two fingers, then switching to grasping it with your whole fist. The dot shakes more when between 2 fingers because your length to diameter ratio is bigger. Likewise, holding just a slug in your chamber is (at least in theory) less stable than holding a slug and cartage. $\endgroup$
    – Nosajimiki
    Aug 6 '21 at 18:43
  • $\begingroup$ @Nosajimiki This works the way it does because the slug can be quite tight in the cartridge neck. You can't just pull the slug out of the case with your fingers -- it's quite a challenge even with pliers. On the other hand, if the bullet is that tight in the chamber of a caseless, you'll need power assist to load each round, which doesn't bode well for functional reliability of semi-auto or full-auto weapons. $\endgroup$
    – Zeiss Ikon
    Aug 6 '21 at 18:47
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What problems still exist for caseless ammunition

cook off

This is the big one, otherwise know as the chamber getting so hot when a fresh cartridge is loaded it discharges, and it is solved by better technology, you need firing chambers that are better at conducting heat and more thermally stable propellant chemistry. Both are doable. C4 is a famous example of an explosive that can be burned without igniting but can be set off with a simple primer.

A chamber that conducts heat better is the best solution but not implemented today because we have only just begun to really learn how to create better thermally conductive materials. But we do have an option, carbon. Carbon nanotube based materials has tremendous thermal conductivity, an order of magnitude or better than the best existing suitable metals, aluminum and steel. To put scale to it the thermal conductivity of carbon structures is better than steel by a larger margin than steel is better than asbestos. It can transfer and thus shed heat unbelievably well. It has this while also being stronger as well. A carbon nanotube firing chamber can dissipate heat fast enough to prevent cook off, in fact it can dissipate it fast enough you might even use existing heat sensitive materials for the propellant. the fact it makes the entire firearm lighter is just gravy. Our current limited ability to manufacture carbon fiber shapes is not something anyone expects to persist long into the future.

Fragility

A common complaint about caseless ammunition is fragility of the ammunition but the most recent LSAT trails show this is largely solved with better chemistry. The military is also less worried about this, since the trend is towards more fragile but cheaper cases, like plastic cased ammunition. since ammunition spends most of its life in containers (magazines or crates) this is not that much of an issue. the only place it really comes up is if a dud round has to be extracted, which is a mechanical problem not a fundamental one, Textron solved it with better extraction methods.

A solved issue is sealing, which has already been solved. existing caseless military trail guns solve it with telescopic ammunition and booster charges, as well as a better design for the bolt and firing chamber, that is just designing it to seal without using a case to cheat.

So really the only change you need from modern caseless rifles is better materials, which is well within our future capabilities.

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