Is this sci-fi weapon realistic?

Question

Image Attribution: The "M50/r Assault Rifle" (Cropped) ©2020 by Supercraft888

Lore and information derived from original work ©2020 by Supercraft888

M36 Rifle

Operation: Select-fire, gas-operated, magazine-feed, ETC

Mass: 2.9kgs (unloaded) 3.5kgs (loaded)

Barrel Length: 50.8cm

Cartridge: 6.8x31mm caseless

RoF: 500rpm (3r) 1800rpm (full-auto)

Effective Range: 10m-980m

Maximum Range: 1,500m

Feed System: 60 round detachable magazine

No. Produced: 180 billion

The Colt M36 Rifle is the standard infantry weapon of UTF forces, including the UTF Army and UTF Marine Corps.

The M36 was designed by Colt Firearm designer Jonathan Stafford in the year 2210. The M36 relies on electrothermal-chemical ignition of cartridges in order to increase accuracy and muzzle velocity, and uses the powerful 6.8x31mm caseless cartridge to deliver powerful kinetic energy into its target.

The M36 is a select-fire weapon, and can be fired in semi-auto mode, 3 round burst mode, and full-auto mode. The weapon also comes with a large selection of high-tech scopes, which can help detect targets, provide aiming assistance, and gives the user information about how many rounds the weapon has left. As of 2259, the weapon is still in service.

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Alright, here’s my question: Is my weapon realistic? Could you realistically get a caseless, ETC Rifle chambered in 6.8x31mm to work?

Answer 1

A few issues

1. Barrel length is very short, longer can easily be achieved by making it a bullpup (as was done in the H&K G11, the only (almost) production caseless weapon to date). This will reduce peak chamber pressure, which is always a good thing for weapon longevity.
2. Effective range of 10-980m - regarding the short range, room clearing will generally occur at less than 10m except for big rooms. 980m is very long for "effective" range for a small round without terminal guidance, as atmospheric variables and resistance will knock it off course and slow it to ineffective speed regardless of how high the muzzle velocity is or how accurately it is fired. (Unless the 980m figure is for use in vacuum and refers to the limits on how steady the weapon can be held.) Add terminal guidance and rocket assist (ie smart bullets - which are a thing) in order to be effective a kilometre out.
3. Rate of fire - As per a comment, it appears that these rates are switched around. 500 rpm is fine for standard full auto, otherwise just wasting ammo. The reason for the 2000 rpm for 3 round bursts for the G11 was to minimise the amount that the muzzle could climb between the first and third rounds so that a 3 round burst at (I think) 300m would all hit a man-sized target if aimed correctly. (Need to dig out my reference books to check my memory on this. Note that the 2000 rpm was for one burst, the effective rate of fire using 3 round bursts would basically be 3 x the rate of firing single shots. Firing a single shot from the G11 apparently felt the same as firing a single shot from a comparable rifle.) Your comments refer to the firer wearing an exoskeleton - if this acts like having the rifle fixed to a bench then possibly a lower rate of fire will allow 3 round bursts to all hit a person-sized target at the same range or the 1800 rpm will allow a 3 round burst to all hit the one target at longer range.
4. Scope - I understand that either an open (holographic?) sight or two different scopes can be attached to the Picatinny rail on top of the weapon, but both scopes appear to have identical characteristics listed. 6x is probably inadequate for engaging targets at 980m. However, I would suggest that by this point there would be one day/night scope with highly variable magnification only, with magnification and crosshairs automatically adjusting based on the range to the target being viewed. Open sights would not be required if this is being used in exoskeleton armour with a helmet, simply project the point of aim onto the user's heads up display (HUC) if they are not using the scope. (Note that scopes like these have been around for a while already, I had a chance to briefly play with one over 20 years ago.)
5. Trigger - there's nothing fundamentally wrong with having a trigger the same as firearms have today, but I would frankly be amazed to see them still being used in 200 years. Squeezing a trigger without moving point of aim is one of the key skills in shooting today, but given that nerve interfaces can be used for basic control of artificial limbs already, I would expect them to be standard for military weapons in 200 years. (Assuming that people are still wielding weapons directly rather than controlling drones that the weapons are mounted on or just delegating the whole business to the robot overlords.)
6. Number produced - 180 billion! Either these are throwaway weapons with a new one issued each day or there's a massive number of highly populated planets with a large proportion of the population armed. It certainly puts the AK-47's production run to shame. The problem with this number of weapons is that if humanity has multiplied so far and so quickly, this is a very tame weapon compared to some of the possibilities being explored today. Examples include Metal Storm and it's pre-loaded barrels of ammunition (change barrels rather than changing magazines), various flechette projectiles etc.

Overall though, there is nothing fundamentally wrong with this design. Very similar to the weapons catalogue from the original edition of Traveller 2300 science fiction roleplaying game back in the 1980s, which was intended to be as "hard" sci-fi as possible except for the "stutterwarp" drive to allow FTL.

Answer 2

• There is a difference between electrical firing of the primer and ETC propellants. Clarify in your text what you mean.
• Not effective below 10m? I would have thought they put some effort into urban actions (or spaceship boarding). Do laser sights come as standards? Wired into the helmet visor?
• The ETC round needs electrical power. Is the battery in each magazine or in the stock? What is the battery capacity?
• Does it make sense to have a conventional-shaped magazine with 60-round capacity? Look at either a drum, or a longer, horizontal magazine on top like the H&K G11 or the FN P90.
• With electric ignition, the cyclic rate should be easily adjustable. So why not a higher rate for three-round bursts and a lower rate for sustained fire? (See the G11 again.)

Answer 3

The least realistic thing is how low-tech it is

By 2210, a weapon this low tech belongs in a museum, not on a battlefield. This weapons is already pretty much doable with today's technology; so, the idea of this being the standard battle riffle in 2210 would be equivalent to finding a muzzle loaded flintlock on the battlefield today. I think for a story set in the very near future, something like this could still make since, but for this to still be an acceptable military grade weapon 200 years from now with all the drone swarms, autonomous kill bots, and power armor being designed right now does not seem very plausible.

If this weapon is standard issue in the future, then it should mean that at some point soon, we will have a major breakdown in society resulting in a technological dark-age, and these weapons would likely emerge out of the Renaissance Era following it... that said, if we hit a technological dark-age, then it is very unlikely that there will be enough people in the future to justify 180 billion of these things. So, if you want your setting to be plausible, you probably need to either rethink the gun or your timeline.

Suggestions for a more futuristic ballistic weapon based on current trends and RnD work

• Autonomous targeting. It is not enough for your scope to just identify threats. It needs to engage them. Many countries are currently working on AI solutions to improve first shot timing to faster than human reflexes would allow. So if your gun sees an eminent threat like a hostile raising his gun to fire on you, it will not wait for you to pull the trigger. It should also be able to find and target specific vulnerabilities. Body armor is improving quickly right now; so, having a weapon system that can find and target the gaps in an enemy's defenses will be important.
• 1 scope to rule them all. The scope should not need to come in 3 sizes. We've already miniaturized optics well enough that a single scope can easily fit many lenses and sensors. It should have a wide range of zooms. It should be able to detect the whole EM spectrum so that you don't need sperate IR or radio scopes. It should be able to use sound to map out parts of the environment that can not be seen in the EM spectrum and to alert you of nearby chatter, heartbeats, and footsteps that are too quite to hear. Maybe it can "smell" too so that it can alert you of the presence of biochemical weapons, or let you track an enemy's footstep like a dog. Get creative with it. The most important part of modern warfare is seeing before you are seen; so, this should be a major area of improvement in the future.
• Guided ammo. The best path to an enemy combatant is rarely a straight line. The current trend of suicide drones is quickly escalating because a drone can attack an enemy around a corner or inside of a trench, which a bullet can not. In the future, this idea should be miniaturized into common munitions such that they should not require line-of-sight anymore. As soon as you detect a threat using one of many possible networked sensory methods. You should be able to fire a projectile that will hunt down the target where ever he may be.
• Don't do caseless ammo, this is a dead-end technology. While caseless ammo allows you to pack more bullets into a clip, a more important feature will be not needing to fire as many bullets to neutralize an opponent. You can only shoot until you are shot; so, if you need to fire 10 times to hit an enemy, but they nail you with the first shot, then they win, even if you started shooting first. As technology makes 1-shot-1 kill more doable, the emphasis will shift more and more towards this META. Caseless ammo (as in the kind where you embed your slug in a solid-state explosive) imparts the most possible heat and percussion into the slug as possible making smart bullets less doable. Instead expect your future tech bullets to more closely resemble tiny missiles than modern bullets. This would still technically be caseless, in the since that there is no cartridge to eject, but a term like micro-missile or micro-drone would more accurately convey this meaning.
• Make the whole system bigger and heavier. The 6-8kg weight of the modern battle riffle is based on what a human combatant can comfortably wield, but your future battlefield should have ubiquitous power armor and/or genetically enhanced soldiers. This means that your "infantry" will be able to carry far more firepower and armor than they can today. So, heavier riffles designed to be held-by and overcome heavier armor will be the norm.
• Automatic ammo selection. Since the gun can be bigger, this also gives you the option to load multiple ammo types at once. If you pair autonomous engagement with differing ammo types, then a solider no longer has to change clips when the threat changes. You could fire 3 smart bullets around a wall to take out an enemy ambush, then fire a burst of flack rounds to take down an incoming drone swarm, and then fire a metallic-hydrogen HESH round to take out an armored vehicle: all without stopping to think about what kind of bullet he is firing.

A final consideration: even if you have a much larger population in the future, don't expect to need 180 billion riffles. Modern warfare is requiring more and more technology and training than it did in the past. A hoard of untrained men with guns is no longer a meaningful threat against drone-swarms, cluster munitions, and ever more tactically skilled professional solders. Instead expect the roll of "infantry" to dramatically change. It will no longer be a squad of humans carrying riffles, but a single human field commander guiding the actions of his squad of various AI powered killing machines much like how 6th gen fighter jets are being designed as command and control platforms for "loyal-wingman". So, even if the human population is 1000 times greater in the future, the number of people who need to carry a hand-held riffle into battle will likely decrease, and your actually ubiquitous battle riffle will be a thing you mount to a droid, not fire by pulling a trigger.

Answer 4

You have a problem with the ammunition weight. The difference between loaded and unloaded weights is 0.6Kg, 600g. You have to fit the magazine and 60 cartridges into that. If the magazine is ignored, the cartridges only weigh 10g each.

Current bullets (just the bullet) for 6.8mm rifles weigh 9g. Making them lighter makes it hard for them to achieve your claimed effective range, and it also looks hard for 1g of propellant to throw a bullet that far, no matter how clever your ETC system is. Your ammunition is going to weigh more than your current figure.