I have one problem with the "impact" argument. Following Newton any round fired from a man-held gun will deliver more energy to the one firing it, than the target it hits (since flight though air reduces bullet velocity). So the only difference between shooter and target are: 1. the hit will be concentrated on a small area on the target (negated by good armor) 2. the target get's hit suddenly in an unexpected place, while the shooter expects the recoil in his shoulder, but this sets a limit to bullets with the impact power to break bones...

@Falco Above all, from the shooter point of view, the impact is diluted in time. The acceleration is more or less uniform on the barrel length (let's say 1m) while a so called "perfect" armor stop it in a few millimeters (or else, there is some penetration). This impact would cause shockwave in the whole object. Also there are recoiless guns and kinetic missile

@Madlozoz you are right, the impact timing is essential. A good armor would also need to disperse the impact over several milliseconds in time, by "slowly" deforming. Recoilless guns are possible, but a lot less practical than normal guns and with kinetic missiles we're already in the realm of shaped charges or other "active" projectiles.

@Falco As others have noted, the shooter can spread the impulse over a longer time, while impacts are more or less instantaneous (particularly if the round doesn't penetrate at all). You can use a long-barrelled weapon, and more exotic things like ETC or even railguns to apply force over time to get greated velocity at less recoil. There's also the option of things that keep accelerating after release, like rockets, missiles, or gyrojet rounds.

About incendiary weapons, it might be worth researching how much asphyxiation would be an issue. Fire tend to be pretty efficient at replacing oxygen with less-than-breathable gazes. Unless the armor is airtight and has its own oxygen supply, that might be another vulnerability.

Blunt force trauma on the target but not the shooter already is the case today. If you do it properly firing a modern rifle won't cause any significant bruising to the shooter; stopping a 5.56/7.62mm rifle bullet on a hard plate will at a minimum result in serious bruising to the person shot and can break ribs.

Alternatively go chemical warfare. Mustard gas need a completely different protection than kinetic projectile. Last I heard, making something bullet proof and gas proof is extremely cost prohibitive.

And while we have treaties against certain types of ammo, the moment a country believes that they'll be destroyed if they don't have it, they'll use it anyway. If it wins you the war, nobody's going to punish you for it. (as long as you dont have large international organizations with a combined military bigger than yours which WILL intervene.)

@Gloweye Or that country just wants to have the weapons. See: the list of treaties that the USA refuses to sign and/or ratify, including bans on landmines, cluster munitions, and anti-ballistic missiles, to name a few - and that's not to mention the various treaties on nuclear weapons tests, or their withdrawal from the Rome Statute.

I can't remember the title, but I once read a story where the battle armor was so tough that nothing could penetrate it, but that didn't stop concussive force and other impact trauma from reaching the person inside. There was a scene where the armory tech, who was a morbid, black humor sort said that the only repair a particular suit needed was a garden hose to wash out what was left of the former wearer.

Depending on the composition of the Armour there may be ways to inflict damage using Spalling which is the mechanism used by HESH rounds, historically used as a way of damaging tanks with thick armor in the 1950s.

@Falco in addition to the time factor already mentioned, some weapons have devices that mitigate recoil, such as a spring loaded piston that travels backwards in the weapon, further spreading out the time of impact.

Fire, in form of napalm/etc, can also damage inner parts of ammor unless the shell is magically solid. Alternative would be to use toxic gas, radiation (if known at the moment).

@nasch that's a good point. I wonder if similar physics could not be used in personal armor. Tanks already have active (ablative) armor, a futuristic armor could also absorb the impact and use a counter impulse to reduce concussive forces 🤔

Re: thermal weapons, don't forget microwave weapons

@Falco. Two solutions: bazooka and gyrojet en.wikipedia.org/wiki/Gyrojet. Both throw the recoil momentum away in propellant gas going the other way...

+1, even if I expected another link about "hammer time"

@Madlozoz In addition to the impact time factor, there's also an energy factor at play here. A bullet that weighs 1/10 of the gun weight will be ejected with 10x the recoil velocity of the gun (due to conservation of momentum), but since kinetic energy is proportional to the square of velocity, it has 100 times the kinetic energy of the recoiling gun. The bullet carries far more energy to its target than the recoil does to the shooter.

@DJohnM Recoilless rifles also exist. They are open on both side and eject masses from both sides (typically, it eject hot gasses from behind) en.wikipedia.org/wiki/Recoilless_rifle

For rifled rounds, twist also plays a factor in the penetration capability. So while a particular piece of armor might be able to withstand an impact from a round with 1:9" twist, might not stop a round fired from a weapon with the barrel designed to twist the round at 1:7". Additionally, the reason modern battle/body armor works is that the ceramic shatters. The kinetic energy of the bullet is dissipated from a single vector to many vectors and the Kevlar weave helps keep the Soldier from being lacerated by the shattering ceramic. Which means the armor is nearly useless after X hits.

Also for your alloy, it has to be forged somehow, So if it can be smithed, it can be hammered flat...increase the velocity of your rounds such that the tin can the man is in hits flat on him. If it cannot be molded by "hammering" then it will likely shatter with sufficient impact. It's either malleable or hard, and it can have some of both, but there are limits.

I would like to add, the armour is made of highly advanced carbon materials like graphemes an CNT.