Fun With: Powered Armor & Tanks

[Howedar]

He doesn't have to. The idea is still absurd.

Would you care to point out what you consider "absurd" about the revised concept, and why?

You mean other than the fantastic expense these suits are going to require compared to the cost it would take to defeat one, the insane ground pressures you're already talking about, or the asinine handwavium you're emitting whenever a problem gets pointed out?

[Feil]

He doesn't have to. The idea is still absurd.

Would you care to point out what you consider "absurd" about the revised concept, and why?

A force that costs less can do the same job better. And that's all there is to it.

[Sea Skimmer]

I was going to get into that in this discussion next - what sort of shells would you envision the coilgun using?

With a velocity of mach 12 any real life material would shatter on impact with armor, though it would have so much kinetic energy that it might still cause massive damage. I’d expect you’d have two basic kinds of ammo. A simple slug of tungsten or even just steel for close range fighting, and a fin stabilized tungsten sabot round for longer range engagements.

Thank all of you for your responses so far. Consider the following revisions to the above description for the armor, then:

- 45-50kph running speed (no jet-boosted running)

That’s still faster then any human can run, which still requires that the suit moves the users limbs for him, which will still do horrible things to his joints. I you want a suit worn like armor and not piloted with a control panel then the running speed cannot be higher then the human maximum. For a 100 meter dash the world record works out to be around 35kph.

[rhoenix]

Alright, how about for 1.5g, or 2g acceleration?

Even with computer control, accelerations like this are going to make it difficult to select a site and land properly. If these jets are used regularly the accident rate will be horrendous.

Furthermore you're proposing over a tonne of thrust out of a couple of tiny nozzles. The jet blast is going to be extreme (i.e. a major hazard and location giveaway even without the thermal and noise signature), and unless you're using some sort of unobtanium to do this with non-thermal thrusters the exhaust is going to be extremely hot and likely set anything around the takeoff or landing sites on fire.

and replacing them with the repulsors, above.

Which are handwavium, but you still have to power them and high speeds still run into the 'landing safely' challenge.

I see what you mean, now - thank you for the detail.

In that case, I'll keep it at 1g acceleration maximum for the reasons you described, and use repulsors instead of jets.

There would be less scattering and it would be at a lower frequency (i.e. UV). Using X-rays means you get less armour/cover penetration (closer to the surface deposit visual spectrum lasers have with the usual problems that entails). At low energies x-rays would be better for anti-personnel work, but energies sufficient to kill another power-armoured trooper this is a non-issue. Gamma rays intense enough to melt armour will give anyone who gets a mild dose (e.g. a grazing hit, or shot through cover that absorbs most of the beam) radiation sickness, unless your EM shielding can stop that.

Fascinating. Thank you for explaining that.

Can you see any issues with using batteries to power the suit (and activate the gun)?

Only that there is little difference between a super-high-energy-density battery and an explosive. Any sort of ion-based system (i.e. anything like current battery chemistries or supercapacitors) is quite likely to short out and release all of its stored energy in one spectacular blast if seriously damaged. You might be better off with some sort of magic power transmission system, powering the suits from reactors in nearby APCs.

Hmm, the energy supply requires greater thought, then.

As for the "beamed power" effect, would this have to be a continuous connection, or just to recharge? In this, I'm assuming you mean something similar to a laser thermal type of system.

Additionally, are there any other ways you can think of for the suit to have enough power to operate both suit and gun for a minimum of a week? Using the Atomic Rocket site for ideas, I'm not seeing very many feasable options.

===

You mean other than the fantastic expense these suits are going to require compared to the cost it would take to defeat one,

Which would be justified if the suit I'm refining, with the help of everyone who's posted so far, can perform well enough. As I said above, this would be intended for the use of elite infantry.

the insane ground pressures you're already talking about,

Would you mind elaborating on what you mean by "ground pressures?"

or the asinine handwavium you're emitting whenever a problem gets pointed out?

Admittedly, there is more than a little handwavium within the design of the suit, but as long as it's internally consistent physics-wise, which is why I posted this asking for people's thoughts in the first place, then it's a small thing.

As for me justifying certain things to other people's questions in this thread with handwavium, would you care to point out what I handwaved that was not later fixed, or made more consistent?

[rhoenix]

A force that costs less can do the same job better. And that's all there is to it.

This suit is intended to be a both ground, and space-based directed assault. If this one design can handle both just as or almost as well as two different specialized designs for ground work, as well as space work, then it would end up being the cheaper option.

===

With a velocity of mach 12 any real life material would shatter on impact with armor, though it would have so much kinetic energy that it might still cause massive damage. I’d expect you’d have two basic kinds of ammo. A simple slug of tungsten or even just steel for close range fighting, and a fin stabilized tungsten sabot round for longer range engagements.

That makes sense to me.

What about a HE type of shell? Or would most of them, barring M/AM shells, be irrelevant in the face of the material hitting at mach 12?

That’s still faster then any human can run, which still requires that the suit moves the users limbs for him, which will still do horrible things to his joints. If you want a suit worn like armor and not piloted with a control panel then the running speed cannot be higher then the human maximum. For a 100 meter dash the world record works out to be around 35kph.

Alright, so the running speed would be about 30-35kph, then. That's still good enough for me.

[Starglider]

In that case, I'll keep it at 1g acceleration maximum for the reasons you described, and use repulsors instead of jets.

Having a humanoid shape fly through the atmosphere (presumably in an upright position) at high subsonic speeds is going to have serious drag, stability and control problems however you cut it. There really isn't any need for 500 km/h speeds. On an open battlefield where that kind of speed would actually be useful, your power armoured troops are likely to be picked off like clay pigeons by enemy light AA fire. Presumably they have repulsor APCs and repulsor tanks for serious maneuver warfare. If you're going to have a flight system, it really only needs to go up to 100 km/h ish (which likely extends your flight time too), and indeed even if faster speeds were possible you'd probably want to limit them to that (or lower!) for safety reasons. Can you imagine a bunch of average soldiers goofing off in suits capable of 500 km/h at 1 metre altitude? The results are not likely to be pretty.

As for the "beamed power" effect, would this have to be a continuous connection, or just to recharge? In this, I'm assuming you mean something similar to a laser thermal type of system.

That requires line of sight to the APC more often than not, which is impractical. If you've already invoked cheap, compact, high-power neutrino radiators, I suggest you just add 'neutrino absorbers' and 'neutrino beam power transfer' and hope you don't get too many physics graduates reading your work . As a bonus you can piggyback your unjammable (though probably not untracable, unless the beam forming is 100% efficient) comms onto your obstruction-ignoring beamed power system. You'd want a small internal battery, in case the APC gets blown up (hopefully there will be another one nearby that can start sending you power on demand).

Additionally, are there any other ways you can think of for the suit to have enough power to operate both suit and gun for a minimum of a week? Using the Atomic Rocket site for ideas, I'm not seeing very many feasable options.

Not really. Advanced nanotech might make aneutronic microfusion practical (but won't solve the waste heat issue). Antimatter is a bad idea for a whole host of reasons. The other options all involve lots of handwavium; minature total conversion reactors, hyperspace taps, power packs that store energy in exotic but non-volatile states of matter, that sort of thing. Even though it's handwavium I like beamed energy because it implies interesting tactical limitations; your power-armoured troops might be frighteningly effective at urban combat, but pick off the support vehicles powering them (and probably all the UAVs as well) and they quickly become normal infantrymen wearing several hundred kilos of scrap.

Would you mind elaborating on what you mean by "ground pressures?"

As in, if you concentrate half a tonne of suit+fuel+ammo+infantryman weight onto 0.25 m2 or less of foot area, they will sink up to their waist if they try to move over soft earth or sand.

[Starglider]

A force that costs less can do the same job better. And that's all there is to it.

Manufacturing cost as we know it isn't necessarily relevant for sci-fi socities. If you've got fully automated manufacturing, particularly general purpose nanoassemblers, it may well be that the only issues are time, energy and the amount of raw elements required. For small-scale military applications this could easily mean that the only real constraint is the mass and volume your transport capability can place in theatre (of the system itself and any supplies/spares it requires).

your power-armoured troops might be frighteningly effective at urban combat, but pick off the support vehicles powering them (and probably all the UAVs as well) and they quickly become normal infantrymen wearing several hundred kilos of scrap.

By which I meant, 'the reactor/generator vehicles are probably powering UAVs, combat robots and light weapons emplacements as well as the power armoured troops'.

[rhoenix]

Having a humanoid shape fly through the atmosphere (presumably in an upright position) at high subsonic speeds is going to have serious drag, stability and control problems however you cut it. There really isn't any need for 500 km/h speeds. On an open battlefield where that kind of speed would actually be useful, your power armoured troops are likely to be picked off like clay pigeons by enemy light AA fire. Presumably they have repulsor APCs and repulsor tanks for serious maneuver warfare. If you're going to have a flight system, it really only needs to go up to 100 km/h ish (which likely extends your flight time too), and indeed even if faster speeds were possible you'd probably want to limit them to that (or lower!) for safety reasons. Can you imagine a bunch of average soldiers goofing off in suits capable of 500 km/h at 1 metre altitude? The results are not likely to be pretty.

I see your points. In that case, keeping the 1g acceleration but reducing the (sane) maximum speed to about 200km/h, with a typical cruising speed of 100km/h.

That requires line of sight to the APC more often than not, which is impractical. If you've already invoked cheap, compact, high-power neutrino radiators, I suggest you just add 'neutrino absorbers' and 'neutrino beam power transfer' and hope you don't get too many physics graduates reading your work . As a bonus you can piggyback your unjammable (though probably not untracable, unless the beam forming is 100% efficient) comms onto your obstruction-ignoring beamed power system. You'd want a small internal battery, in case the APC gets blown up (hopefully there will be another one nearby that can start sending you power on demand).

That's brilliant, I must say. I'll tentatively use that as the power system, and do a few write-ups. This also necessarily changes the design of APC's for this universe as well.

Not really. Advanced nanotech might make aneutronic microfusion practical (but won't solve the waste heat issue). Antimatter is a bad idea for a whole host of reasons. The other options all involve lots of handwavium; minature total conversion reactors, hyperspace taps, power packs that store energy in exotic but non-volatile states of matter, that sort of thing. Even though it's handwavium I like beamed energy because it implies interesting tactical limitations; your power-armoured troops might be frighteningly effective at urban combat, but pick off the support vehicles powering them (and probably all the UAVs as well) and they quickly become normal infantrymen wearing several hundred kilos of scrap.

Which actually, I like, and it makes sense with a few other parts of their technology. In keeping the total weight of the suit now at 25kg, including gun and ammo, that's not too bad if the light goes out - it's just now somewhat cumbersome armor - and your gun now has a very limited number of shots before it stops working.

As in, if you concentrate half a tonne of suit+fuel+ammo+infantryman weight onto 0.25 m2 or less of foot area, they will sink up to their waist if they try to move over soft earth or sand.

Good point, but in the revision above, I had reduced it to 10kg for the suit itself, another 8kg for the gun, and about 5-6kg for coilgun ammo, totalling about 25-26kg. With that reduction in weight, would you foresee any issues with ground pressure?

[rhoenix]

By which I meant, 'the reactor/generator vehicles are probably powering UAVs, combat robots and light weapons emplacements as well as the power armoured troops'.

That does change things a bit. The APC's are necessarily going to require much heavier armor and shielding, thereby requiring a larger power plant, just to supply power to all the ground-combat robots, UAV's, and light weapon emplacements. However, this is still a very good restriction, and I like it.

[Admiral Valdemar]

It sounds like we're going to end up with the suits Reynolds has in his novels. They were typically not much taller than a human, just bulkier enough to carry the needed technology. They were frog like in shape when unused and moved up to and engulfed the pilot from behind, using sensors to adjust suit measurements to fit snugly before couplings fastened and shape memory materials melded round the front and sealed.

The suits were able to give several days of endurance with waste and nutrition systems. They filled with a liquid air fluid to compensate for high-gee manoeuvres, since the suits were powered by anti-lithium cells large enough to give sufficient power to go up to 10 g before the pilot was knocked out due to lack of ability at such extremes (the on-board AI took over in other words). The suit could use a retractable umbilical to harvest any heavy particles for propellant. For atmospheric flying, the suit morphed to a delta like configuration with the pilot facing down and forward, arms flush and melded with the sides and legs melded together (the vernier/main propulsion thrusters were two in the heels and one in the mid-back).

Weaponry was often morphed out on the arms and shoulders and computer targeted. Everything from variable spectrum lasers to particle beams, railguns or "Ack AM" guns which fired anti-proton beams could be used independently. The tips of the arms, although often featureless flippers, could form digits of any needed type. The suit's skin is normally plain white and could be altered to act as an active camouflage to blend with the surroundings, though not as therm-optics from what I recall.

I think that is pretty much the best you can get without magic. Heinlein's stuff is also good, notice the fact that they used jump jets there. They didn't fly and they didn't, hilariously, run at 500 KPH. Bouncing is as effective as you'll get without pure flight, which with such a small package, will be hard unless you use AM or have absolutely tiny fusion power plants of great efficiency.

This all depends on your tech level and mission. These suits were more like wearable micro-spacecraft since no one had fighters because, well, capital ship weapons can swat them from the sky anyway.

At the end of the day, these suits must be because you need humans for something or to have them overlook a dangerous battle being fought by machines. For each of these suits, the weakest link is the human. You can make much smaller, cheaper robotic drones so long as you have the AI and don't require humans actually be on the battlefield for anything else.

[Starglider]

That does change things a bit. The APC's are necessarily going to require much heavier armor and shielding, thereby requiring a larger power plant, just to supply power to all the ground-combat robots, UAV's, and light weapon emplacements. However, this is still a very good restriction, and I like it.

Actually this is a good application for tanks in urban combat. They probably have bigger reactors than the APC/IFVs; they are heavier, have more shields, have much more energetic main weapons etc. However in urban terrain a tank rarely uses its full speed or its main armament. So it should have a lot of reactor capability left over, which this technology could put to use.

I had reduced it to 10kg for the suit itself, another 8kg for the gun, and about 5-6kg for coilgun ammo, totalling about 25-26kg. With that reduction in weight, would you foresee any issues with ground pressure?

No but if the whole suit weighs 10kg, including artificial muscles, jump jets, sensors, controls, comms, beamed power reception etc, then the armour plating can't be more than 5kg. A contemporary Interceptor vest with a full loading of hard inserts weighs 15kg and only protects the torso from rifle cailbre fire. Your armour is supposed to protect against GPMG rounds at twice current muzzle velocities, about 12 times as much protection over twice as much surface area at one third of the weight. This is probably physically possible but only with advanced nanotechnology (e.g. ring carbon composite).

Incidentally I strongly suggest you take a look at these pages;

Feasiblity and Characteristics of Powered Armour

How Armour Works

Ultrastrong materials

[Starglider]

Two specific things you might like in the above powered armour page;

Ramshell accelerators - coilgun like velocities but with no power demands (however lower accuracy, higher signature and higher ammo weight)

Superconducting loop power storage - note that to be practical this requires room temperature superconductors (which are unobtanium, particularly if they have a sufficiently high critical magnetic field density to work as really high density power stores) and it suffers from the same 'serious damage will probably cause it to explode' problem as a super-capacity battery, though it will probably be a bit more robust.

[Feil]

This suit is intended to be a both ground, and space-based directed assault. If this one design can handle both just as or almost as well as two different specialized designs for ground work, as well as space work, then it would end up being the cheaper option.

Which is why submarines can fly and tanks are neutrally buoyant.

Specialization decreases cost and increases performance in the specialized area. There's no reason for a ground pounder to carry an oxygen supply, insulation against unfiltered solar radiation, and a pressure suit. There's no need for a moon fighter to have the ability to deal with the weight of his suit under one gravity, a weapon with significant recoil, a rocket recharger that only works in atmosphere, and soundproofing over the ears to survive the twelve sonic booms he generates every time he fires his weapon. A soldier who doesn't have to carry things he doesn't need can carry more things he does need. A soldier who has the things that he needs is better than a soldier who doesn't. And that doesn't even begin to address the added cost of making something dual purpose. Again, consider the flying submarine and the submersible tank.

[Starglider]

Which is why submarines can fly and tanks are neutrally buoyant.

Your general point is correct but it may not apply here.

There's no reason for a ground pounder to carry an oxygen supply,

The suit will have to be NBC sealed anyway. In an interstellar setting it will probably need to work on planets that don't have breathable atmospheres (e.g. mars for a start). Making it a pressure suit with an oxygen supply wouldn't take much extra effort. If the oxygen cylinders are removable (which they should be for easy recharging) you can always leave them at home on missions that don't need them.

insulation against unfiltered solar radiation,

They probably already have radiation protection to a much higher standard if grasers are a standard battlefield weapon, and/or tactical nukes and AM weapons are being thrown around regularly.

There's no need for a moon fighter to have the ability to deal with the weight of his suit under one gravity,

It's true that the extra strength to negate the weight of the suit is probably useless in zero G, particularly if it's only an extra 10kg.

a weapon with significant recoil,

The weapon is almost certainly going to be mounted on the suit, not an integral part of it, and as such could be easily changed.

a rocket recharger that only works in atmosphere,

This is probably the biggest issue. Jets that work well for atmospheric flight are not going to be good for space maneuvering.

[rhoenix]

It sounds like we're going to end up with the suits Reynolds has in his novels. They were typically not much taller than a human, just bulkier enough to carry the needed technology.

I haven't read very many of his books, but I did see them used in Diamond Dogs, which also gave me inspiration for mine - I didn't know that they had all those other capabilities as well.

I think that is pretty much the best you can get without magic. Heinlein's stuff is also good, notice the fact that they used jump jets there. They didn't fly and they didn't, hilariously, run at 500 KPH. Bouncing is as effective as you'll get without pure flight, which with such a small package, will be hard unless you use AM or have absolutely tiny fusion power plants of great efficiency.

Yes - the running speed in my concept (since I cannot edit the OP) has been reduced now to 30-35kph, without any jet-assisted running.

This all depends on your tech level and mission. These suits were more like wearable micro-spacecraft since no one had fighters because, well, capital ship weapons can swat them from the sky anyway.

True. In the universe I'm using this armor in, the only fighters used are drones, so this makes sense.

At the end of the day, these suits must be because you need humans for something or to have them overlook a dangerous battle being fought by machines. For each of these suits, the weakest link is the human. You can make much smaller, cheaper robotic drones so long as you have the AI and don't require humans actually be on the battlefield for anything else.

This is actually a good point, and the thing that could force Occam's Razor to frown on the suit. On the other hand, if humans at this level of technology ventured out only if necessary themselves and usually let robots to the physical stuff, then this suit comes back into favor, being useful for a variety of environments while protecting the wearer.

===

Actually this is a good application for tanks in urban combat. They probably have bigger reactors than the APC/IFVs; they are heavier, have more shields, have much more energetic main weapons etc. However in urban terrain a tank rarely uses its full speed or its main armament. So it should have a lot of reactor capability left over, which this technology could put to use.

This is an excellent point, and one that would reduce the number of needed vehicles, as well.

No but if the whole suit weighs 10kg, including artificial muscles, jump jets, sensors, controls, comms, beamed power reception etc, then the armour plating can't be more than 5kg. A contemporary Interceptor vest with a full loading of hard inserts weighs 15kg and only protects the torso from rifle cailbre fire. Your armour is supposed to protect against GPMG rounds at twice current muzzle velocities, about 12 times as much protection over twice as much surface area at one third of the weight. This is probably physically possible but only with advanced nanotechnology (e.g. ring carbon composite).

There is nanotech in this universe I'm designing this, but having it be this refined might have unintentional effects on the rest of the faction in question, so I'll hold the weight above as tentative - as you say, for it to protect as well as the OP, it'll most likely have to either weigh more from the armor, or less and rely on the EM and particle shields for defense. This also makes it more vulnerable in hostile environments, which is why I'd lean toward it weighing more, in light of your point.

Also, thank you for the links you provided - fascinating reading.

===

Specialization decreases cost and increases performance in the specialized area. There's no reason for a ground pounder to carry an oxygen supply, insulation against unfiltered solar radiation, and a pressure suit. There's no need for a moon fighter to have the ability to deal with the weight of his suit under one gravity, a weapon with significant recoil, a rocket recharger that only works in atmosphere, and soundproofing over the ears to survive the twelve sonic booms he generates every time he fires his weapon. A soldier who doesn't have to carry things he doesn't need can carry more things he does need. A soldier who has the things that he needs is better than a soldier who doesn't. And that doesn't even begin to address the added cost of making something dual purpose. Again, consider the flying submarine and the submersible tank.

Starglider addressed most of your points before I did, but I will say that this was intended for use in a variety of environments and atmospheres. This is a military exploration suit.

You do have an excellent point about the jets requiring an atmosphere - but this is another reason I'm now going with using repulsors instead. It'll have much lower speeds (200-250kph maximum speed, with a 1g acceleration) than indicated in the OP, but it'll also work in space and planets with oxygen-thin atmospheres as well, which is something I didn't notice before while designing it.

[Starglider]

but this is another reason I'm now going with using repulsors instead. It'll have much lower speeds (200-250kph maximum speed, with a 1g acceleration) than indicated in the OP, but it'll also work in space and planets with oxygen-thin atmospheres as well, which is something I didn't notice before while designing it.

'Repulsors' generally repel mass. You generate lateral thrust by pointing them at an angle, so that they're repelling the ground to one side of you rather than directly below you. There's no mass to repel in space; even if you're in low orbit and the repulsors can reach right down to the planet, you're screwed if you want to move /towards/ the planet.

I think what you want are 'inertialess thrusters' not 'repulsors'. Obviously this has major implications for your starship sublight drives. Repulsors and some types of anti-gravity have a range (i.e. altitude) limit that preserves the distinction between armoured vehicles and aircraft/aerospacecraft, but inertialess thrusters do not, so there may be no difference between an APC and a dropship, or a tank and a fighter/bomber in your setting (i.e. it may look like the Scholock Mercenary universe.

Personally I like to have a distinction between low-altitude-only, relatively slow moving heavily armoured vehicles and aerospacecraft that use atmospheric lift and jets/rockets, so I tend to go with limited-range mass repulsors (which can operate on the same principle as the near-mandatory artificial gravity, just in reverse). Space maneuvering thrusters can be ion engines, you don't need anything like as much thrust.

[Admiral Valdemar]

I'd really avoid anti-gravity/inertialess drives. Those things butcher physics like nobody's business and give you the ultimate KE weapon to boot.

I've not been a fan of AG after finally looking at what it means and how experiments have proven the area rather fruitless. Now, playing with gravity other ways, maybe. Just no massless drives.

[Starglider]

Gah sorry 'reactionless thrusters' even. Inertia control is a seperate (and even less plausible) concept.

I've not been a fan of AG after finally looking at what it means and how experiments have proven the area rather fruitless. Now, playing with gravity other ways, maybe. Just no massless drives.

Some way of exerting attractive and repulsive forces at range, such that you can have repulsors and artificial gravity, is ok as long as it respects conservation of energy and momentum (and preferably, has a limited range). Anti-gravity in the sense of 'somehow avoiding the usual effects of being in a gravity field' is more troublesome.

[Admiral Valdemar]

Actually, I think inertialess gets more interest today than AG for research. Though by "inertialess", I mean lowering practical mass effects to a degree, since obviously having no inertia means bad things happen.

Assuming a field could be made and your biologic pilot was hardy enough, I bet you could skim a few kilos off and aid agility.

And hey, at the end of the day an aerofoil is anti-gravity and it's cheap.

[Starglider]

[quote="Admiral Valdemar"Though by "inertialess", I mean lowering practical mass effects to a degree, since obviously having no inertia means bad things happen.[/quote]

It is almost impossible to reconcile inertia control with conservation of energy, as past threads on this board examining Trek 'mass lightening' technology have illustrated.

[Admiral Valdemar]

Someone seems to think there's still something in it. There were a couple of papers on what gives mass and whether it can be manipulated on Ars Technica and NASA's site a while back. I chalk it off to the Pentagon route of try-everything-just-to-be-sure. Metric altering is probably magic you don't want to toy with, like messing up E=mc^2.

I could at least see how lowering mass effects could work out, rather than a drive that doesn't seem to do anything out the nozzle. Sadly I find AG and massless drives are a brain-bug now.

[Sea Skimmer]

That makes sense to me.

What about a HE type of shell? Or would most of them, barring M/AM shells, be irrelevant in the face of the material hitting at mach 12?

Well what caliber is the gun supposed to be? You probably don’t have space inside the projectile for a worthwhile HE payload and against most targets it wont make any difference. A 150 grain projectile (weight of a .30-06 bullet) at 4000m/s (close enough to mach 12) would already pack 75kj of kinetic energy. If the gun fires heavier projectile, say 700 grains (on par with a .50cal machine gun bullet) then this goes up to 364kj. Thats the kind of firepower a small caliber anti tank gun has in real life.

If you want ammo with a better effect against soft or area targets, then I suggest using a beehive or canister for close range, and shrapnel for long range. These sorts of shells take advantage of the tremendous kinetic energy your bullets already have, by splitting it into many smaller sub projectiles. Shrapnel bursts with a time fuse, canister and beehive break up the monet they leave the barrel.

The difference between beehive and canister BTW is that beehive uses a crapload of small finned darts while canister uses a bunch round balls. In terms of the effect on soft targets there isn’t much to choose from, but canister seems to have won out in real life.

The suit and gun will have only limited ammo, because of bulk even if weight doesn’t matter, so probably only two types of ammo are ever carried at one time. I'd expect the discarding sabot AP round would always be carried, to deal with enemy vehicles and other armored suits, while the secondary type of ammo would be chosen based on the expected mission.

Some specialist high tech ammo might also exist, like a radio jammer shell or sensor shell. These would probably be carried and loaded individually, and would be fired at lower velocity so they don't dig deeply into the ground on impact.

[Starglider]

The difference between beehive and canister BTW is that beehive uses a crapload of small finned darts while canister uses a bunch round balls. In terms of the effect on soft targets there isn’t much to choose from, but canister seems to have won out in real life.

The drag on a small projectile with a high surface area to mass ratio has to be pretty extreme at mach 12. Pellets are going to melt and possibly vaporise within a pretty short distance. Darts will fare better, but I imagine they'd have to be made out of tungsten or something more exotic to survive the heating effects (and this doesn't include any inductive heating they get in the accelerator).

I'd expect the discarding sabot AP round would always be carried,

Which should be either a superconducting or hypermagnetic sabot for a coilgun.

Some specialist high tech ammo might also exist, like a radio jammer shell or sensor shell. These would probably be carried and loaded individually, and would be fired at lower velocity so they don't dig deeply into the ground on impact.

/Much/ lower velocity.

Some sort of grenade launcher might also make sense, one or two to a squad, for indirect fire capability.

[Admiral Valdemar]

Do we want coilguns or railguns? Personally, if you can make materials this good, the ablation problem from railguns, already fairly minimal now, shouldn't be an issue and the higher velocities attained would be a great advantage.

Coilguns do have their own perks too, I guess this hinges on how you want the weapon to function and for what.

[Starglider]

the ablation problem from railguns, already fairly minimal now

WTF? The ablation issues with railguns are enormous, and the main reason they haven't been fielded yet, and Rhoenix is proposing higher muzzle velocities for his infantry weapon than current naval/artillery-scale prototypes can achieve.

shouldn't be an issue and the higher velocities attained would be a great advantage.

Why do you believe railguns produce higher muzzle velocities? If anything it should be the reverse.