"Infantry" main weapons for the setting described below?

Question

What would be a suitable choice for "infantries" (the quote unquote is because it is not necessarily a real person, possibly just a rover with a gun doing the job of a footsoldier) for this following setting? the general background, especially the technology, is a bit messy with a mix of near, mid and far-future tech that I'll attempt to outline below (for example a capital ship in the setting belonging to the state might have a antimatter beam-core engine while it's missiles are methalox/Metallic Hydrogen rockets launched from a coilgun and communicating with other ships with lasers then gitting a reply with neutrinos)

assumptions:

1: The function of the civilisation being discussed (hereby referred to as the state)'s infantry is much like today's, namely fighting in buildings, tunnels, forests etc where armor and artillery is either unavailable or need some support, alongside with holding these regions

2: The opponent is also human, however as they're interstellar colonists who had no contact with the state for roughly three hundred years, the state is as familiar with them as the Aztecs are familiar with the conquistadors. They relies on infantry far more than it does on armored vehicle or artillery (if this sounds awfully world war 1 to you, you're absolutely correct, because the vast majority of their wars are either purely space combat or really didn't call for more than infantry). They have little automation so robotic enemies are out of the question. Their infantry is protected either very poorly with little to no protection at all, with heavy armor that would be considered NIJ standard type IV armor by modern standards, or force fields that could be depleted with 20 hit from 12.7s while being armed with star wars Blaster-like weapons. Their force fields could stop a single EMP or electrocution attack by taking it for whatever it is protecting once and getting disabled as a result.

3: The infantry (alongside with anything that is intended to be used on the surface) is deployed using Project Orion style dropships capable of landing with large payloads around 200 tons. However due to the fallout of detonating nuclear devices as thrust, the infantry may only leave while inside their IFV or APCs (which also means that unless otherwise specified, the infantry is always expected to have their vehicle somewhere nearby to support them)

4: The state as a whole utilizes only technology that would be considered unobtanium at most (for example a Kerr-Newman black hole on a vessel is fair play but a lightsaber is not), handwavium is avoided with the possible exception of negative mass

5: while most of the fighting is on shirt-sleeve habitable planets, it is also required to be able to function in non-habitable environments such as a methane atmosphere (though it does not have to function in vacuum)

6: The state considers it's army (space force not included) to be largely expendable in the sense that they would try to force the enemy into attrition warfare if it believe it could win one, does not care much about public relationships (this is after all a totalitarian regime), and draws from a larger overall manpower/resource pool than it's opponents possibly could. However when on the offensive they tend to have less units immediately available due to having rather expensive transport costs, therefore superior individual performance is desirable

7: the state has very capable and portable power sources that could be scaled down to infantry use in the range of 10-30 megajoules per kilogram

8: Powered armor(or exoskeleton, depending on how yo classify them) exists, they could provide a large amount of power to the soldier's equipments, and the state could afford to equip a large amount of it's soldiers with them. However they are much less capable than astartes. They are capable of boosting mobility and firepower but anything that will cause a individual soldier to be heavier than 235KG will not be accepted, in order to not collapse the floor/stair they might be standing on (if they can't enter a building safely than there's no reason for them, why not bring in a tank?). They only provide armor in critical areas such as the chest, and no radiological protection beyond what is expected from a HAZMAT suit (although this does make them impervious to chemical weapons). On the other hand they are notably un-bulky compared to the traditional image of powered armor, appearing simply to be a slightly higher soldier (the closest example I can think of is Iron Man)

In responce to the situation being described above, what could the state's infantry be primarily armed with? (Just the "assault rifle", more specialized weapons such as anti-armor is a totally different issue, which I also happen to be more confident in)

(At GMT time June 19th, this post was reopened despite the author having already reposted according to a senior member/moderator's advice, and the second post seems a lot better answered.)

Answer 1

As you have described the problem, the answer is a standard, Modern AR-15 style rifle

From a technical stand point, the evolution of the intermediate cartridge (7.62 Russian, 8mm Kurz, .223, 5.45 etc.) was because post WW2, they found that most Infantry on Infantry engagements took place within 400m and having a full-power service round (.303 British, 8mm Mauser, .30-06 etc.) that was effective out to longer distances but had additional weight for the same number of rounds, additional recoil and a number of other issues that were not offset by the greater stopping power and range that they provided.

And this is why I am writing this answer, more as a Frame Challenge - Infantry weaponary is always a balancing act.

As a case-in-point, the US Army with the NSGW program has switched to the .277 Fury round because the experience in Afghanistan (and the widespread use of Optics) have pushed the standard engagement distances further out, where the .223 was loosing effectiveness.

Rather than have us brainstorm what futuristic weapons you might have (which is against site rules anyway) - you should ask yourself this:

• What is the function of your Infantry in your world?
• What tactics does your Infantry use?
• What opponents or enemies are your Infantry expected to fight?
• How does your Infantry deploy?

To give some context to the above - I am going to reference one of my favourite fictional worlds: Warhammer 40K. In case you are not up-to-speed, I will outline two of the human factions - the Adeptus Astartes (The Space Marines) and the Astra Militarum (the Imperial Guard).

The Space Marines are genetically engineered super-soldiers in Power armour. They use the Bolter - which fires a .75 rocket-assisted projectile, that functions as an APHE round (Armour piercing, High Explosive) - it has a small time-delay fuse - so that it explodes inside the target. In Universe, Bolters are complex and difficult to manufacture and have a lot of recoil.

The Space Marines are the tip of the spear - going into the toughest areas, surrounded by enemies on all sides - so they need to be able to inflict maximum carnage, both in actuality but also psychology, to break the will of the enemy to fight. Their Weapons fulfill their mission requirement and role on the battlefield

The Imperial Guard soldier on the other-hand has the Lasgun (mockingly called a Flashlight in-lore owing to its poor damage output) - It is easy to produce and maintain, uses standard powercells and whilst one Lasgun is not the most effective weapon, the IG are designed to fight in massed ranks with artillery or tank support, so whilst one Lasgun is not that effective, 10,000 Lasguns firing in sustained Volleys is quite effective. Their Weapons fulfill their mission and their role on the battlefield

Answer 2

Californium nuke rifles

Exotic isotopes can have critical masses well below uranium. For examples, californium 252 has a critical mass of 2.7 kilos. With futuristic compression, neutron deflectors, and tampers you might be able to get that down to 2 kilos or less. That means you can have a miniature nuke you can fire for around 2 kilos. With AI assisted software to fire it, you could hit anything within 400 meters, and anything close to it, and software on the bullets could adjust their yield.

This should beat most armour and would be very effective at area denial. Futuristic anti radiation nanites could repair the damage to the infantry person who needs to repair broken bullets or guns.

Answer 3

• Launchers for small guided/homing missiles, using both on-board sensors and data network from the infantry trooper, UAVs, and other missiles. This could be a backpack with a vertical launch system or something rifle-shaped.
  Possibly it works like a grenade launcher and the missile gets an initial boost from that.
• Rifles with caseless ammunition, a bit like the H&K G11.
  This could be built completely without electronics, networked or otherwise, and invisible to some kinds of sensors. Assume that it is not acceptable for a force to simply shoot any human, and that more modern weapons allow the wielder to be identified as a combatant more easily.
• A coilgun with a little automated forge/lathe to turn metal bars into ammo. The hit probability is enhanced by a computerized sight. The battery can be recharged from the power grid.

Answer 4

There is no need to ask this question in the speculative mode, for the infantry battles of your likely future are already raging all around you. If your planetary civilization survives past infancy, the distinctions between military drones, biological weapons, and cyberweapons will soon melt away. Combat will come to resemble ant colonies clashing over a food source, bracken and heather struggling for territory, a virus invading a multicellular organism's distributed firmware, a power grid battling a local desynchronization, or arbuscular mycorrhizae defending a grassland against locusts. The job of a foot soldier—to maintain effective control over territory—will descend to the microscale and the nanoscale, where it will be taken on by more agile, more distributed weapons systems.

Answer 5

With such a large amount of energy available, a coilgun with cartridges involving frozen gases and a super hot chemical propellant. The propellant explodes like gunpowder, both accelerating the frozen gas and heating it to plasma levels. This ionized, superheated gas is then further accelerated by the electromagnetic coils and drawn by the magmatic field into a stable donut shape, which moves faster than a bullet to the target, where it would either supercharge a shield, causing it to restart or break entirely, or burn a hole through whatever flesh or metal is in the way, decimating flesh. Unfortunately the range of such a weapon is rather low, as the plasma dissipates as it flies, and metals with higher melting points would not melt and give way as easily, but against modern armor and in close range, an automatic version of this would work well. However, this would be a specialized anti-infantry weapon, so a normal railgun or coloring might be more believable in the use of a modern state used to symmetrical warfare.