The Caseless Ammo Weapons Issues and Solutions

[TeufelIV]

For a story I have been working on I wanted to use caseless ammo weapons. The increased fire rate and decrease of casing are intriguing. However I have noticed a few problems with the ammo and weapons that I have been trying to hash out. I want to try and work these out because I want some believability in my writing without just simply waving it on through the story. I am operating on the lines that ballistic explosively propelled weapons are simply efficient and as technology marches on can only improve. The big limits are still recoil, heat, and ammo weight.

The two big issues with the caseless ammo and weapons are excessive heat and fouling.

It turns out the brass cartridges perform a bit of a crucial role as a removable heat sink for the weapon. The process of the shell being extracted and ejected also serves to cycle some air into the weapons in addition to the casing carrying away waste heat. This is actually very serious issue for the weapon design. It became hot enough in some tests for a round to possibly cook off in the chamber. The cook off issue was solved via changing the propellant to a higher grade explosive propellant with a higher ignition temperature. However this does not fully solve the heat issue just the cook off. The weapons still get very hot. The heat of firing can case increased barrel wear, damage of plastic components, and increase the chances of barrel warping from long periods of sustained fire like say in a long fire fight or a pitched battle.

The fouling issue is from the weapon being so sealed up that it traps a lot of the carbon fouling produced from firing. This is also partially solved by the higher grade propellant but still does not remove the issue. This means the weapon needs to be dissembled and cleaned very thoroughly. Also the build up of carbon increases weapon wear and can hinder proper function of the moving parts. Again the act of ejecting a casing allowed some of the waste gas from firing that is not used in operating the weapon to escape the weapon. Please no systems that rely on direct impingement.

I have discussed this before with friends, colleagues, and folks on other forums. No one can really offer some good ideas to solve these issues.

Here are the best answers I have found through the various discussions.

For the Heat

• Reduce the fire rate for fully automatic fire and burst fire. This can be tied into the heat sink cartridge additive solution.
• Introduce a heat sink component to the caseless cartridge that is ejected as part of the cycle of operation.
• Some sort of possibly exotic air cycling that is part of weapons function that vents heat. This could also possibly be used to reduce the amount of waste gas cycled back into weapon during firing.

For Fouling

• The above mentioned air cycling scheme to help vent some of the waste gas and fouling out of the weapon.
• The propellant is so high quality it reduces the overall fouling and reduces the time between cleaning cycles.
• A operating system like in a piston system of modern weapons reducing the amount of fouling that even reaches the rest of the weapon.

Pros and Cons of the solutions.
Heat

• Pro:For the cartridge heat sink. The advantage would be making a tailor made substance/material that could maximize the heat absorption and allow a lot of waste heat to be ejected. It also does not completely negate the advantages of shortening the cycle of operations if weapon design is altered to take it into account.
• Con: For cartridge heat sink. Normal cycle of operations Feeding, Chambering, locking, firing, unlocking, extracting, and ejecting is shortened mechanically to exclude the extracting and ejecting phase. Not only is the mechanical energy for these processes now used to simply restart the cycle it removes mechanical pieces that can break from weapon. Namely the extractor/ejector portion. The heat sink in the cartridge could possibly be designed to be ejected straight from it's position after the round has been fired. This however reintroduces the ejecting phase of the cycle of operations. This slows the weapons fire rate and adds in mechanical function that requires parts that need maintaining. Also it is possible for the heat sink to be jammed somehow during the ejection process.
• Pro: Air cycling system. Again it is technically feasible to introduce this to the weapon. The increased air circulation could not only carry away fouling gases but could leech a lot of heat into the air.
• Con: Air Cycling System. This leaves the open open to elements and increases exposure to environmental conditions that can lead to increased issues with the weapon especially in harsh environs. If air and gas can get in/out so can dust, dirt, and debris.

Fouling issue

• Pro:High Quality Propellant; This is fairly easy to do and make the weapon work with the powder design.
• Con: The higher quality propellant might noticeably increase ammo cost and might be issues with those who skimp on the ammo and use lower grade propellant. Very similar to what supposedly was one of the big issues with the earliest issue of the M-16 family of rifles.
• Pro:Piston system. This a very tried and tested system that still works. With advances in mechanics, metallurgy, and other systems related to the weapons this can become very efficient if designed well. Also the weapons chamber and barrel pressures will be higher possibly leading to a increase in muzzle velocity and or round hitting power.
• Con: Piston System. More mechanical parts, the barrel, chamber, piston, and bolt mechanisms have to be more rugged to handle the higher pressures generated by the system. The higher pressures may also increase muzzle climb and weapon recoil if not properly countered.

So any ideas? Additional Pros and cons?

[Rabid]

Just questions :

Heat :

Can the bullet itself be designed as to serve as some sort of heat sink ? Say like adding some copper fins at the end of the bullet fixed on a little copper rod, in conjunction with a smooth bore cannon. This would also give you a higher muzzle velocity, I think.
And the fins could also be designed to enhance the "tissue damages" once the tip of the bullet has penetrated the ballistic protection of the enemy combatant.

As for the heavy machine-guns with a high rate-of-fire, couldn't they be water/oil-cooled ? Or is it too technically difficult / a pain in the ass on the field ?

[folti78]

Just questions :

Heat :

Can the bullet itself be designed as to serve as some sort of heat sink ? Say like adding some copper fins at the end of the bullet fixed on a little copper rod, in conjunction with a smooth bore cannon. This would also give you a higher muzzle velocity, I think.
And the fins could also be designed to enhance the "tissue damages" once the tip of the bullet has penetrated the ballistic protection of the enemy combatant.

Nope, the bullet already carries away it's share of heat, but the problem is the remaining hot gases in the chamber, which heat up the chamber and the barrel, instead of heating up the case (which are promptly removed along with some of the hot gases still in it). Of course you might try to design a system which pumps air into the chamber, to force the gases out, but it'll come with the standard cost of complexity and reliability.

As for the heavy machine-guns with a high rate-of-fire, couldn't they be water/oil-cooled ? Or is it too technically difficult / a pain in the ass on the field ?

Liquid cooling is heavy, you have to lug around the coolant too and if it's an active system, the extra parts of it, like pumps, hoses/pipes, heat exchangers, batterypack. If you use a simple passive system (like the early machineguns, with a water tank encasing the barrel), it only acts as a simple puffer until the water boils and then you are back to square one, with an extra time penalty for having to wait for the water puffer to cool down too. This was the constant problem of the early machineguns during sustained firing, where the crew had to improvise additional cooling methods (pouring water, putting bags of ice or in some cases, literally pissing on it). No wonder that lighter machine guns started to use different methods to prevent overheating (examples: reducing the rate of fire, forced air cooling or quick change barrels).

[TeufelIV]

Yeah I already decided liquid cooled systems are mostly a no go for the reasons we stopped using them. The added weight and extra logistics for the weapon made them difficult to move around. I had considered possible exotic methods of coolant like a liquid metal or other substance but as noted above once it gets too hot it can take a while for it to cool off enough for use.

I had very briefly considered making a ejectable heat sink that is part of the weapons magazine but you know lots of heat near the ammo not a good thing and making the magazine hot would make it difficult to extract by hand if problems arise.

I was tempted to use the heat sink system like Mass Effect uses but that is logistically forcing you to carry more crap and again leaves really hot things that need handling if something goes wrong.

[folti78]

Yeah, the same effort you want to invest into making a workable caseless ammo and gun would probably give you some lighter casing material, that still can work as a removable heatsink. Otherwise we are back to the case that the only viable solutions would be reduced ROF with with specially designed heat transfer mechanisms*, which dump the heat into the other parts of the weapon. Might work with weapons not designed for continuous fire(handguns, semiauomatic rifles, assault rifles without the full auto mode.)

* something like a simple metallic heat conductor, nothing more elaborate.

[Swindle1984]

The newest version of the M-60 has a carbon-fiber reinforced barrel that is less prone to overheating. Belt-fed machine guns tend to change barrels every 200 rounds or so to avoid overheating; one demonstration of the new barrel had them fire 800 rounds with one pull of the trigger and no malfunction or loss in accuracy due to heat. Building the barrel and chamber out of heat-resistant materials could work.

Alternately, many older machine guns used fins as heat radiators (and they did actually work, to a degree), and the Lewis Gun had a tube around the barrel; when it fired, the muzzle blast would create a vacuum at the end of the tube and suck air in and out of the tube, contributing to a cooling effect. It didn't do a lot, but it did help some. The Spectre M4 submachine gun has a specially designed bolt that pumped air through the jacket around the barrel to help cool it; obviously a caseless gun isn't going to work that way, but something similar could work.

The only caseless assault rifle I know of in real life, the G11, did indeed have a low rate of fire compared to conventional assault rifles: 400 rpm as opposed to the 600 to 700 rpm most use. It also had a burst function that fired three rounds at 2,000 rpm (the same rate as a minigun) and a recoil reduction system that prevented the user from feeling recoil until the third round fired; this effectively put three bullets in roughly the same hole every time you pulled the trigger, very handy for penetrating body armor.



So, in summary, your caseless assault rifle of the future can be handwaved to be made of materials less prone to overheating and ammunition with higher ignition temperatures to avoid cookoffs, the gas can be diverted to not only cycle the weapon but also help cool it, and the gun can fire at lower rates to reduce temperature increases. This lets, say, a rag-tag group of guerrillas have a decent chance against troops with the latest, greatest guns because even though theirs are heavier, bulkier, and hold less ammunition, they have a higher rate of fire and are less vulnerable to overheating.

It's a nice balance of advantage vs disadvantage.

Another thing you have to consider: how vulnerable is your caseless ammunition to humidity?

[TeufelIV]

I had forgotten about the latest gen M-60. I have seen that video and it is impressive. I know about the radiator fins to aid in cooling by exposing more surface area to the air. Modern mortars have them for the same reason.

Yeah if I really wanted to I could just point out advances in various fields allows the caseless weapon to handle higher tempratures and greater stresses. Hmm the question is which materials to choose. I am sort of leaning on some sort of composite material.

Those rates of fire are pretty nuts. I am guessing the reduced full auto rate is for heat and recoil control. From what I remember the weapon cycles so quickly that the full effect of the recoil is as you noted not felt til the third round. I am betting that is also part of the weapons frame design. There were two other neat recoil compensation systems I ran across. One was in the Ak-100 or 101 I think? The other in the Kriss Vector SMG. It uses a mechanism that redirects some of the kinetic energy downward reducing muzzle climb.

Thank you for reminding of the other big issue with the ammo the caseless weapons. The casing provides both protection for the powder, structure, and ensures a good seal with the chamber. They could of course make the casing out of something that is combustible with the propellant and booster charge ignition.

What about say having the bullet itself double as the casing and ammo. Some sort of ring or hollow spot that contains the propellant and have it be ignited by something like akin to a bbq starter?

I noticed on the G11 ammo there is a plastic cap on the top of the cartridge. Anyone know what purpose that serves?

[Whiskey144]

I noticed on the G11 ammo there is a plastic cap on the top of the cartridge. Anyone know what purpose that serves?

That'd be due to the telescoped nature of the G11's cartridges; the projectile's volume is surrounded by the propellant. This makes it more compact.

What about say having the bullet itself double as the casing and ammo. Some sort of ring or hollow spot that contains the propellant and have it be ignited by something like akin to a bbq starter?

Not quite; a very similar design is already in use on Russian 40mm grenades- they're caseless, but because the propellant is contained in the base. It uses the standard hammer/pin arrangement found in most weaponry.

Note that such a system is very close to be a "rocket-propelled" bullet; it's very similar to what is used in the real-life Gyrojet family and the fictional Bolters of Warhammer 40,000 fame.

[TeufelIV]

Ahh thanks Whisky. I was sort of thinking about the Gyrojet projectiles sans the rocket boost.

What about electronic ignition systems like in Metal Storm and certain Auto cannons?

The one other interesting ignition method I know of was used for a Daisy .22 Caseless ammo gun. It used compressed air ignition. Basically the compression of the air in the chamber heated up enough to ignite the propellant. No primer needed.

[Starglider]

Liquid cooling is heavy, you have to lug around the coolant too and if it's an active system, the extra parts of it, like pumps, hoses/pipes, heat exchangers, batterypack.

Closed-cycle systems certainly seem impractical. However for an automatic rifle, how about open cycle phase change cooling from a small vial of perfluorohexane (or similar non-corrosive, non-flammable, low boiling point liquid) in the magazine? The coolant mass required should still be lower than the casing mass, because evaporative cooling (exhausing down the barrel) will suck out more joules than conduction to metallic casings. The solvent properties of this kind of coolant might even help with the carbon fouling, although that could cause problems with lubrication.

[TeufelIV]

That is actually an interesting and novel solution. You could have the vial as part of the magazine under some sort of pressure that forces it into a cooling sleeve directly around the barrel or chamber. There could be a simple pressure valve that if enough of the pressure from evaporated coolant would push the vents open and as soon as pressure in the coolant chamber normalized it would shut the valve again.

I am assuming it is feasible to measure the amount of fluid needed in vaporization could more or less accurately measured for the the total number of rounds in a given magazine.

That might actually work quite well for heavy weapons as well.

Let me know what you folks think on that pressure control idea for a cooling sleeve.

[Winston Blake]

The fouling issue is from the weapon being so sealed up that it traps a lot of the carbon fouling produced from firing. This is also partially solved by the higher grade propellant but still does not remove the issue. This means the weapon needs to be dissembled and cleaned very thoroughly. Also the build up of carbon increases weapon wear and can hinder proper function of the moving parts. Again the act of ejecting a casing allowed some of the waste gas from firing that is not used in operating the weapon to escape the weapon. Please no systems that rely on direct impingement.

I don't see how a caseless firearm is any more 'sealed up' than a cased-ammo one. In my view the ejection process itself has negligible effect on fouling. Ultimately some residual gas must escape out the ejection port of a direct impingement systems, but this is just an incidental peculiarity of that kind of system.

For the Heat

• Reduce the fire rate for fully automatic fire and burst fire. This can be tied into the heat sink cartridge additive solution.
• Introduce a heat sink component to the caseless cartridge that is ejected as part of the cycle of operation.
• Some sort of possibly exotic air cycling that is part of weapons function that vents heat. This could also possibly be used to reduce the amount of waste gas cycled back into weapon during firing.

(1) is sensible but I expect you want to maximise performance.

(2) is unclear - I don't see any advantage of this over water-cooling.

For (3), the Lewis gun and Spectre SMG have been mentioned - I will also mention the Pecheneg GPMG. It uses a modern Lewis-like design, with a much 'tighter' shroud and a ribbed barrel. It apparently works well for cooling.

For Fouling

• The above mentioned air cycling scheme to help vent some of the waste gas and fouling out of the weapon.
• The propellant is so high quality it reduces the overall fouling and reduces the time between cleaning cycles.
• A operating system like in a piston system of modern weapons reducing the amount of fouling that even reaches the rest of the weapon.

For (1), I don't think this effect is a problem in the first place.

For (2), this seems perfectly reasonable. The G11 had very clean propellant, but I don't know if this was a solution to any actual fouling problem or merely an incidental development.

For (3) yes, anything other than direct-impingement gas-operation will have less fouling (all other things equal). Even delayed blowback weapons aren't as bad. Piston-based gas operation is probably still going to be the best bet in the future.

Pros and Cons of the solutions.
Heat

• Pro:For the cartridge heat sink. The advantage would be making a tailor made substance/material that could maximize the heat absorption and allow a lot of waste heat to be ejected. It also does not completely negate the advantages of shortening the cycle of operations if weapon design is altered to take it into account.
• Con: For cartridge heat sink. Normal cycle of operations Feeding, Chambering, locking, firing, unlocking, extracting, and ejecting is shortened mechanically to exclude the extracting and ejecting phase. Not only is the mechanical energy for these processes now used to simply restart the cycle it removes mechanical pieces that can break from weapon. Namely the extractor/ejector portion. The heat sink in the cartridge could possibly be designed to be ejected straight from it's position after the round has been fired. This however reintroduces the ejecting phase of the cycle of operations. This slows the weapons fire rate and adds in mechanical function that requires parts that need maintaining. Also it is possible for the heat sink to be jammed somehow during the ejection process.

This has no advantage over water cooling, and has greater mechanical complexity as you have alluded to. Water has a very high specific heat capacity and a water-cooling system can condense steam and re-use it. These 'heat sink cartridges' seem to be intended to use special material and be wasted like cases. Further, water can be obtained anywhere, including by urinating, as was used for Vickers guns in emergencies.

[*] Pro: Air cycling system. Again it is technically feasible to introduce this to the weapon. The increased air circulation could not only carry away fouling gases but could leech a lot of heat into the air.
[*] Con: Air Cycling System. This leaves the open open to elements and increases exposure to environmental conditions that can lead to increased issues with the weapon especially in harsh environs. If air and gas can get in/out so can dust, dirt, and debris.[/list]

I think a Pecheneg-style design is perfectly adequate for this. Further, most (all?) machine-guns in the world are open-bolt, and they get by just fine, so I don't think dirt ingress is a big deal. If it's a big deal in your scenario (alien worlds?), then having a closed-bolt option for harsh environments may be worthwhile, at the cost of RoF and a small increase in complexity.

Fouling issue

• Pro:High Quality Propellant; This is fairly easy to do and make the weapon work with the powder design.
• Con: The higher quality propellant might noticeably increase ammo cost and might be issues with those who skimp on the ammo and use lower grade propellant. Very similar to what supposedly was one of the big issues with the earliest issue of the M-16 family of rifles.

Yeah, it's a trade-off of cost vs performance. If your scenario is set in the future, I can see ultra-low-fouling propellants being cheap.

[*] Pro:Piston system. This a very tried and tested system that still works. With advances in mechanics, metallurgy, and other systems related to the weapons this can become very efficient if designed well. Also the weapons chamber and barrel pressures will be higher possibly leading to a increase in muzzle velocity and or round hitting power.

I think piston systems are already about as efficient as they can get - it's just a piston driven by expanding gas. I don't see why the chamber or barrel pressures would be significantly higher, or why muzzle velocity or energy would be higher. The portion of propellant energy used to drive an action is tiny.

[*] Con: Piston System. More mechanical parts, the barrel, chamber, piston, and bolt mechanisms have to be more rugged to handle the higher pressures generated by the system. The higher pressures may also increase muzzle climb and weapon recoil if not properly countered.[/list]

I don't see why it would necessarily have more mechanical parts. You need a bolt carrier anyway, and as in the AK, the piston can be combined with the bolt carrier as one part. I also don't think it would need to be more rugged than other types of action. Although the AK is rugged and has 'bad' recoil, this is largely a result of Soviet engineering philosophies rather than any inherent characteristic of piston-gas-operated actions.

Just questions :

Heat :

Can the bullet itself be designed as to serve as some sort of heat sink ? Say like adding some copper fins at the end of the bullet fixed on a little copper rod, in conjunction with a smooth bore cannon. This would also give you a higher muzzle velocity, I think.
And the fins could also be designed to enhance the "tissue damages" once the tip of the bullet has penetrated the ballistic protection of the enemy combatant.

No, I don't think so. Even in this case, the rear of the bullet still has only a small fraction of the total area exposed to hot gas, and this fraction drops rapidly as the bullet moves up the barrel. A 'fin-based bullet' wouldn't work for smoothbore barrels - the fins would have negligible effect. You would want a flechette instead, so the oncoming supersonic airflow can actually 'reach' the fins. For a bullet-shaped object, stabilising surfaces behind the shock cone won't work until after it drops below the speed of sound.

As for the heavy machine-guns with a high rate-of-fire, couldn't they be water/oil-cooled ? Or is it too technically difficult / a pain in the ass on the field ?

Yes. It adds complexity and reduces ease of operation somewhat, but it is perfectly technically feasible. In the early days of machine guns, they were all water cooled.

If you use a simple passive system (like the early machineguns, with a water tank encasing the barrel), it only acts as a simple puffer until the water boils and then you are back to square one, with an extra time penalty for having to wait for the water puffer to cool down too. This was the constant problem of the early machineguns during sustained firing, where the crew had to improvise additional cooling methods (pouring water, putting bags of ice or in some cases, literally pissing on it). No wonder that lighter machine guns started to use different methods to prevent overheating (examples: reducing the rate of fire, forced air cooling or quick change barrels).

I don't think this is correct, although I don't understand what you mean by a 'puffer'. Maxim guns and related designs continuously condensed and recycled the water - there was no 'going back to square one after the water boils'. There is a case where Vickers guns were fired continuously for 12 hours, with barrels only changed after each physically wore out. They lost water gradually over time, but this was due to imperfect recycling efficiency over long periods. To be honest I don't know why Maxim and Vickers guns lost water over time - I would have thought 19th Century engineers could easily make well-sealed pressure vessels, etc. My guess is that they lost good-sealing due repeated thermal expansion & contraction.

Yeah I already decided liquid cooled systems are mostly a no go for the reasons we stopped using them. The added weight and extra logistics for the weapon made them difficult to move around.

What exactly is your scenario? Whether or not liquid-cooling is worthwhile depends entirely on the application. For example, fighting off massive alien human-wave horde attacks would be a great application for water-cooled MGs. I can't back this up, but I am fairly sure that the death of the water-cooled MG was due to a change in tactical doctrine. I.e. small, highly mobile groups fighting other small, highly mobile groups don't want or need hours-long-bullet-spewing emplacements.

I had considered possible exotic methods of coolant like a liquid metal or other substance but as noted above once it gets too hot it can take a while for it to cool off enough for use.

I had very briefly considered making a ejectable heat sink that is part of the weapons magazine but you know lots of heat near the ammo not a good thing and making the magazine hot would make it difficult to extract by hand if problems arise.

I was tempted to use the heat sink system like Mass Effect uses but that is logistically forcing you to carry more crap and again leaves really hot things that need handling if something goes wrong.

This sounds like a bad idea. The Mass Effect concept is not realistic - it would require supertechnology to work. Water has a very high specific heat capacity, and if you imagine a system which automatically changes-out 'water catridges' as they become 'full of heat', then that's conceptually identical to a water-cooled system.

Another thing you have to consider: how vulnerable is your caseless ammunition to humidity?

To add to this, physical fragility of caseless rounds is a problem. The G11 was supposed to keep its ammo in either magazines or surrounded by plastic in clips. Humidity-degraded propellant may cause failures, and cracked propellant may cause catastrophic failures due to an excessive burn rate (unlike in powder-form cased cartridges). These could give important plot points. It's worth investigating the robustness of the G11 ammo, and also that of the Voere rifle. Of course, if desired, you can handwave it and say that chemical engineering is awesome in the future so none of these problems apply.

Yeah if I really wanted to I could just point out advances in various fields allows the caseless weapon to handle higher tempratures and greater stresses. Hmm the question is which materials to choose. I am sort of leaning on some sort of composite material.

You may be interested in graphene, which has an extremely high thermal conductivity, and is expected to be pretty useful in the future. Further, all other things equal, a stronger barrel can be thinner and thus improve the rate at which a barrel can dump heat into the atmosphere. Some kind of graphene-reinforced metal-matrix composite barrel may be suitable.

Those rates of fire are pretty nuts. I am guessing the reduced full auto rate is for heat and recoil control. From what I remember the weapon cycles so quickly that the full effect of the recoil is as you noted not felt til the third round. I am betting that is also part of the weapons frame design. There were two other neat recoil compensation systems I ran across. One was in the Ak-100 or 101 I think? The other in the Kriss Vector SMG. It uses a mechanism that redirects some of the kinetic energy downward reducing muzzle climb.

Yes, the G11 had a floating receiver, like the Abakan (another 'super-high-burst-rate' rifle) and the AA-12. The AK-107 and AK-108 use the 'BARS' system. This is essentially an attempt to reduce the recoil disadvantages of the AK's heavy, overpowered, reliable gas system by adding a second opposing piston in front of the existing one. It adds complexity and it's not actually necessary if you use a smaller, 'weaker' system, as in the G36 or other piston-operated rifles. I dislike the 'Vector' - it's an inelegant, bulky, complex, overhyped and theoretically-dubious system. It makes me wonder if it's some kind of investment fraud scheme. I see very little value in it, and I see no reason for you to include such an abomination in your fiction.

My view is that if you want to use high-recoil automatic rifles, a floating receiver and/or a low boreline are the best options. The AR-10 was controllable in full-automatic due to its much lower boreline compared to the M14, and there exist bottom-chamber-firing revolvers with very low borelines which are very controllable.

What about say having the bullet itself double as the casing and ammo. Some sort of ring or hollow spot that contains the propellant and have it be ignited by something like akin to a bbq starter?

Not quite; a very similar design is already in use on Russian 40mm grenades- they're caseless, but because the propellant is contained in the base. It uses the standard hammer/pin arrangement found in most weaponry.

Note that such a system is very close to be a "rocket-propelled" bullet; it's very similar to what is used in the real-life Gyrojet family and the fictional Bolters of Warhammer 40,000 fame.

It was also used in the ancient Volcanic Pistol, called 'Rocket Ball' ammunition. A similar concept was used in the Benelli CB-M2. A basic disadvantage of this is that, except for 40mm grenades, the propellant volume is typically large compared to the projectile volume, forcing the projectile to 'drag along' the empty base section on its flight. It's telling that all of these were pistol or grenade rounds. If you want to use this in your fiction, you need some kind of supertechnological propellant that exceeds the limits of chemical energy density. That would permit the projectile to have only a small 'wasted volume' after firing.

---

TeufelIV, please give us a summary of your setting and your provisional firearm concepts when you are ready. I am interested in seeing how you pull together all the bits of info in this thread.

[TeufelIV]

Wow I am going to have to take a little of time here and go through this all. Thanks for pointing out all spots with trouble.

[Winston Blake]

Liquid cooling is heavy, you have to lug around the coolant too and if it's an active system, the extra parts of it, like pumps, hoses/pipes, heat exchangers, batterypack.

Closed-cycle systems certainly seem impractical. However for an automatic rifle, how about open cycle phase change cooling from a small vial of perfluorohexane (or similar non-corrosive, non-flammable, low boiling point liquid) in the magazine? The coolant mass required should still be lower than the casing mass, because evaporative cooling (exhausing down the barrel) will suck out more joules than conduction to metallic casings. The solvent properties of this kind of coolant might even help with the carbon fouling, although that could cause problems with lubrication.

Closed-cycle liquid-cooling may be practical for rifles if the rest of the weight is reduced enough, for example by use of lightweight materials. Whether this is possible can be dictated by the author. Interesting idea - note that cooling the interior of the barrel directly may cause engineering problems. Normally a barrel heats up and cools down gradually. I don't know what prolonged, rapid heating and cooling on a timescale of tenths of a second would do to a barrel's interior surface. But again, it's something can be essentially dictated by the author based on future technology - it's not a 'science problem', it's an engineering problem.

That is actually an interesting and novel solution. You could have the vial as part of the magazine under some sort of pressure that forces it into a cooling sleeve directly around the barrel or chamber. There could be a simple pressure valve that if enough of the pressure from evaporated coolant would push the vents open and as soon as pressure in the coolant chamber normalized it would shut the valve again.

I am assuming it is feasible to measure the amount of fluid needed in vaporization could more or less accurately measured for the the total number of rounds in a given magazine.

That might actually work quite well for heavy weapons as well.

Let me know what you folks think on that pressure control idea for a cooling sleeve.

A sleeve should work, and avoid the issue I mentioned above. A pressure valve should effectively prevent dirt ingress into the sleeve. However, I feel uneasy about open-cycle cooling - it just seems like a waste to carry around quantities of special liquid which will only be wasted. Some kind of 'limited-performance, lightweight, closed-cycle, passively-pumped liquid-cooling system' would feel better to me, and would have even less dirt-ingress. I think this is about as far as we can go without actually studying this as a proper engineering problem. There are too many unknowns and trade-offs. From here on, author's fiat is adequate for fiction-related purposes.

[TeufelIV]

I don't see how a caseless firearm is any more 'sealed up' than a cased-ammo one. In my view the ejection process itself has negligible effect on fouling. Ultimately some residual gas must escape out the ejection port of a direct impingement systems, but this is just an incidental peculiarity of that kind of system.

Now that I have gone back over some more information it didn't have a fouling problem. I could not find the book I thought I had, that went over experimental and prototype weapons, that stated it did. So I had the wrong information on that. According to the sources the cartridges actually burned rather cleanly. So I don't have to worry about the fouling just the heat which makes this easier. One of their solutions is a new type of explosive propellant.

Having replicated Dynamit Nobel's ACR ammunition, the HITP (High Ignition Temperature Propellant—it is hexogen/octogen based to decrease heat sensitivity) based ammunition was modified to a 5.56 mm round.

From Wikipedia Lightweight Small Arms Tech Page. Best I could find for now. I wear I read something about coating the propellant in something hardened the formed powder and reduced sensitivities to moisture and deformation. Advanced adhesives or other enhanced method of bonding a compound into a solid shape.

On the graphene how would you implement that? Layer in with the barrel design or series of cooling vanes or a cooling sleeve like the Pecheng uses?

A H & K site with the G11

That weapon mechanism looks almost nightmarish. But I am pretty sure that has more to do with mechanism for feeding ammo.

Closed-cycle liquid-cooling may be practical for rifles if the rest of the weight is reduced enough, for example by use of lightweight materials. Whether this is possible can be dictated by the author. Interesting idea - note that cooling the interior of the barrel directly may cause engineering problems. Normally a barrel heats up and cools down gradually. I don't know what prolonged, rapid heating and cooling on a timescale of tenths of a second would do to a barrel's interior surface. But again, it's something can be essentially dictated by the author based on future technology - it's not a 'science problem', it's an engineering problem.

I am starting to like the sound of the cooling sleeve a bit more if we can keep the weight down. Alloys of various materials, advanced plastics etc. The idea I was thinking of is when you seat the magazine it also connects a small pressurized container of coolant that injects a bit of replacement coolant into the sleeve. I can see ditching the on bullet heat sink needing to be ejected. That was the first thing I could think of was adding back in some part of process that helped carry away heat in the first place. Keeps the design simplified and keeps the rate of operation advantage.

Not entirely sure what you mean by passively pumped liquid cooling system. I do like the idea of minimizing ingress of dirt and grime into a weapon. Contaminants increase part wear as a weapon cycles which is part of the reason regular weapons cleaning is important.

A air cycling system kind of like on the Pecheng with those cooling veins sounds like it would well for long barreled weapons like full sized rifles. I am not so sure about carbines but I think a cooling sleeve would work well for those.

Actually now that I think about it, I don't think any modern machine guns fire int he closed bolt. The various weapons that don't are a variety of heavy machine guns and auto-cannons. In WWI some of the aircraft machine guns used closed bolt because it was apparently needed to operate with the interrupter gear and that seems to be last time we used rapid fire weapons like that. I would have keep the closed bolt operation in mind though.

A efficient propellant should be easy to do in a future setting.

On the bolt I was thinking either through some of material or mechanical action to maximize the efficiency of the piston and reduce any noticeable wear and tear on movement of the system.

The reason I was thinking of avoiding using liquid coolant was I was thinking of the total mass and hauling around the water cans made the weapons very heavy. I think the reason the weapons leaked so much was either the hose connection or the pressure from the evaporated water helped cause a leak in a bad or seal some where in the liquid cooling sleeve.

I would agree that desire to be able to move the firepower of a machine gun more rapidly and get it set up rapidly pretty much killed water cooled machine guns.

What is your opinion on the perfluorohexane as a coolant?
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Ok the Summary. It is late and I need to sleep and I spent a bit too much time just writing out this whole post. Pleas forgive me if I mucked it up too much.

Ok a summary of the general story. This is a future setting in which the world has gone through at least two more world wars one of which will use nuclear weapons on a limited scale but the damage to various targets left a lot of problems behind like the destruction of key centers of scientific advances etc. One of the world wars left a lot of unpleasant left overs like automated weapons, genetically engineered predators, and other unknowns on the lowest levels.

Ballistic weapons are still in wide spread use simply because they are easy to make, maintain, and design. Body armor is going to more or less match that advancement. I was thinking Non-newtonian armor plates backed by something resembling a Chobham armor plate are the absolute top of the line armors. Or put the non-newtonian fluid armor behind that armor plate instead.

The U.S. has long since collapsed under the weight of a combination of divisive politics, economic collapse, and outbreaks of internecine warfare between states that control various aspects of various industries giving them a bulk of the power. The focus of the story is in a single massive city that is home nearly 10 million people somewhere in the midwest. Massive towers, arcologies, industrial sectors, and complex and varied transit system make up the city. The city is ruled over by a city council comprised of various powerful, rich, and influential individuals who attempt to maintain a sort of balance in the city while ensuring their specific spots as the heads of said city. Plenty of room for maneuvering and backstabbing.

The main characters are going to be one unlucky sod who gets screwed by the bureaucracy and assigned a dirty nasty job called " Line Men" There job is to go into the now vast tunnel network of sewers, mass rail transit lines, and abandoned tunnels that had been dug over the years. The line men are assigned jobs based on the skill, job completion rate, and gear they have been able to purchase. The machine that does this though has to have the team boss or leader prepare a job request ahead of time to get the more lucrative jobs or it just assigns you the job it thinks you need to do for the day. This is sometimes a crap shoot and the machine malfunctions on occasion screwing them over. They will have to contend with genetically created animals, mutants, aggressive third party interests, organized crime, and a variety of gangs that live in the sub tunnels above the most dangerous zones. The line men are their own culture because they are put in the crappy worker arcologies or housing and do dirty nasty work that needs to be done underground. They have poor life expectancies because of work and health hazards.

Samples of tech are automated weapons, drones, some form of robot, genetically engineered designed animals, there is some higher end energy tech, I want to include power armor but not make it absolute game breaker just a serious force multiplier, I am still toying with the idea of having some sort of automated nano-machine manufacturing being used on a wide scale as well wide spread medical use. The issue is the people who designed it originally have either vanished or withdrawn from society in to the nano-manufacturing facilities and sealed them up so no one can get in. Occasionally someone will be called to the factories and never be seen again.

I wanted to toy with last World War being fought because someone created a very potent Genetically altered human and used a myriad of technology to maximize their abilities. The down side is the creation goes a bit nuts and nearly takes over the world. He uses the populace that sides with him as test subjects to form an army of enhanced humans that run amok on the planet until they manage to kill him. Humans that are genetically altered to be soldiers in a similar fashion are shunned because of this. Somehow these variations are going to start showing up in the population naturally it seems for unknown reasons causing all sorts of problems.

I am thinking of leaving a bunch of this off or playing around with different ideas to see how I might be able to actually use them in the story. By no means is this a finalize decision of how I want things to work.

[Starglider]

What is your opinion on the perfluorohexane as a coolant?

I'd note that flurocarbon based coolants are banned in real life for open-cycle applications due to ozone layer concerns, but no one is likely to care about that in a post-nuclear-war hellhole. I know ozone-safe replacement compounds exist but I don't know the chemistry.

[Purple]

Caseless ammunition is by its nature of being encased in propellant quite brittle and prone to chipping unless you have a custom built loading system. Furthermore, it is much more difficult to produce and store due to the issues you mentioned. Now even if you could correct this quite easily the cost of developing them combined with the cost of developing, producing and maintaining your liquid cooled weapon will be high. So my question is how do you justify using it in a post nuclear environment? Presumably, in such a setting you will see science and technology advancing away from awesome but expensive toward mediocre but cheap. You are much more likely to see AK derivatives floating around than advanced CTA weapons.

[Rabid]

@Purple :

Maybe they where developed before the War, where widely used and distributed during its Conventional phase, and the infrastructure and knowledge necessary to continue production was somehow not totally destroyed during the Holocaust ?

If a 3rd or even a 4th World War was fought, then it is likely that military production and industrial mobilization was very high at the time. As such, there probably was hundreds of millions of weapons produced, maybe even billions, with a good portion still in use to this day, cannibalizing spare parts from the almost inexhaustible stock of surplus weapons from the War era. Plus, it is probable that not all the factories where destroyed, so this can explain that from there on people decided to continue to build "proved and rugged" weapon designs they still had the factories to produce.

So, maybe you are right, and it is indeed "cheap and mediocre" by the standard of the time, the AK equivalent of this timeline - which the possible presence of power armors and maybe even some instances of energy weapons might support.

[Purple]

So, maybe you are right, and it is indeed "cheap and mediocre" by the standard of the time, the AK equivalent of this timeline - which the possible presence of power armors and maybe even some instances of energy weapons might support.

I didn't realize he was going that far into the future. My bad than.

[TeufelIV]

A note; The use of the nukes in war limited to handful of specialized targets that unfortunately takes out a lot of important infrastructure slowing or in some cases halting important research.

I did also note the reason they keep producing the Ballistic caseless weapons was going to be because by this point they are cheap, easy to make, reliable, and fairly efficient. Power armor and energy weapons will be present but only expect them to be fielded by actual militaries.

[Winston Blake]

On the graphene how would you implement that? Layer in with the barrel design or series of cooling vanes or a cooling sleeve like the Pecheng uses?

I honestly don't know. There could be all sorts of problems involved in implementing graphene-reinforced composites. The layers can't be concentric cylinders because the heat won't flow well out of the barrel to the surrounding air, so you may need some kind of multi-layer spiral-like cross section. If I were you I would just assume that graphene tubes or rolls of some description can directly replace carbon fibres in existing composite 'designs'. It may be valuable to research the fibre-winding patterns used in current experimental carbon-fibre-reinforced barrels. Vanes should be fairly easy to implement.

Not entirely sure what you mean by passively pumped liquid cooling system.

I mean a system similar to the Maxim or Vickers, where steam is continuously bubbling up and driving steam out of the jacket into the condenser, as I understand it. Overall, the power for pumping is derived from the hot barrel via the cooling process itself, as a kind of steam engine. In fact it's kinda like a fire-tube boiler, but with only one tube.

What is your opinion on the perfluorohexane as a coolant?

I had never heard of this until Starglider mentioned it. I'm uncertain whether it is better than water at cooling, since water is so good at it.

A quick calc shows that water can absorb significantly more heat. For each, I've assumed 1mL of liquid at room temperature and pressure, which starts at 25º and must be heated to 100º and then vapourised. I.e. 'add 75 K and then add latent heat of vapourisation'.

Water -> absorbs 2574 J per mL.
Perfluorohexane -> absorbs 290 J per mL.

Data for water: SHC,latent heat.
Data for perfluorohexane: latent heat, SHC & density.

So it seems to be greatly inferior at absorbing heat, and is 68% heavier than water. Although it has the advantage of still being able to absorb heat by evaporating at temperatures as low as 56ºC, I don't think that range really matters for gun barrels. If the barrel is at <100ºC then it's in no danger of overheating anyway.

The main characters are going to be one unlucky sod who gets screwed by the bureaucracy and assigned a dirty nasty job called " Line Men" There job is to go into the now vast tunnel network of sewers, mass rail transit lines, and abandoned tunnels that had been dug over the years. The line men are assigned jobs based on the skill, job completion rate, and gear they have been able to purchase. The machine that does this though has to have the team boss or leader prepare a job request ahead of time to get the more lucrative jobs or it just assigns you the job it thinks you need to do for the day.

This sounds like a good setting for game. The part about entering the 'lines' of transit/transmission/communication reminds me of Metro 2033. If you haven't heard of that it may be good reference material.

[Starglider]

So it seems to be greatly inferior at absorbing heat, and is 68% heavier than water.

That coolant is used for electronics because it's non-conductive and non-reactive. Water is a great coolant but I thought there might be corrosion problems blasting superheated steam down the barrel; you also have to allow for it condensing and pooling in the action. That said with futuristic materials technology a fully waterproof barrel lining is probably not a problem. Just make sure you use distilled water to avoid limescale buildup in your gun

[Dwelf]

Have you considered integrating the heat sink into the clip itself. You can embed a solid state heat transfer backbone into the weapon that the clip connects into. Ideally artificial diamond but copper would do fine. The waste heat is then used to melt a solid embedded in the clip so you don't have to worry about pressure build up too much while gaining the benefit of using energy to change the substances state. If you use some form of electricaly detonated propelant it should be possible to make it sufficently thermally resistant.

Since you don't vent the coolant you don't need to worry about fouling a pressure valve. Once cooled the clips can be reloaded if desired and since they have no complicated moving parts dropped into a bucket of water to cool faster. If you need extra cooling on larger weapons you can have extra connectors to attach removable heat sinks. A simple red LED would be sufficient to indicate that the heat sink is at capacity or if your feeling fancy an automatic monitor could detatch it.

[Purple]

A question. Once you do all that you will end up with a weapon that is bulkier, heavier and more mechanically complex than a modern rifle by maybe as much as 2-3 times. So is the gain of using caseless ammo really worth the trade off?

[Simon_Jester]

Yeah, what are the advantages of caseless, and what are they really worth? The main one I've heard of, and I could be wrong about this, is weight savings on a per-round basis.

For the Heat
[*] Introduce a heat sink component to the caseless cartridge that is ejected as part of the cycle of operation.

...Wouldn't this, in effect, mean turning caseless ammunition back into cased? Making the heat sink a cylindrical case wrapped around the propellant seems like about the most efficient way possible to achieve this result, and we already do it.

Fouling issue
[*]Pro:High Quality Propellant; This is fairly easy to do and make the weapon work with the powder design.
[*] Con: The higher quality propellant might noticeably increase ammo cost and might be issues with those who skimp on the ammo and use lower grade propellant. Very similar to what supposedly was one of the big issues with the earliest issue of the M-16 family of rifles.

The increased cost also becomes an issue if the main reason to use caseless ammo in the first place is weight savings- each soldier is carrying more rounds, and the cost per round increases because of the quality control issues.