Ed: This is my first post here so sorry for any mistakes I made. I realize my question was kinda stupid thinking about it.

Here's the gist, I'm having issue coming up with a round for standard infantry that is capable of penetrating some body armors designed. These armors are built with precision and complexity, made of nano-machined ceramics in a crystalline pattern as is capable of stopping most body armors and taking quite a bit of force. There's also some that use more metal like ceramics. Both have some other elements to them, but the most important thing is their protection level, being rated to withstand a high power rifle round like .338 lapua magnum, and have a fair level of protection against laser based weapons through high heat capacity and cooling systems. I could get into the specifics, although that isn't incredibly relevant. The main gist is just rounds with high penetrating power in a reasonable package. Now, I'm trying to design something that's capable of penetrating that. I've tried a few things so far, but have scrapped most of them for varying reasons, those things are:

  1. Flechette weapons. This would be something like the Steyr ACR, using a typical rifle round, but instead of a typical bullet, a high speed flechette instead. This would have sufficient penetration, but had major defects like not working very well in rain, and not doing much body damage.
  2. SLAP-like ammunition. I've heard of SLAP ammunition in the past, and heard it was used for standard rifles rounds like 7.62 NATO and could increase penetration. The reason I passed on these is that they're not very effective in small calibers and suffer from inaccuracy
  3. Squeezebore rifle. This is something I always tend to like to come back to, just since I think it's such an interesting design by nature. It has some viability, but is offset by it's short barrel life and suffers from inaccuracy in small calibers.
  4. Gyroget rifle. The main possibility I saw here was the theoretical capability of high speeds, but was off put by it's low fire rate, low reliability, and just bad performance.

I've also thought through some other possibilities, although I haven't thought them through too much and I'm not sure if they would work very well or not. These are:

  1. Railgun/Coilgun Rifle. I presume I could get sufficiently high speeds out of a railgun or coilgun, although the main flaws I see are high power draw from them and the issue of using them for infantry weapons, but otherwise a possibly good candidate.
  2. A typical gun with a coilgun enhancer. This is very similar to the one above, but I think it also seems promising. It has less power draw than a typical coilgun, but the major downside is the necessity of the round to be magnetic, ergo limiting the round in terms of options. A possibly work around would be an iron jacket around a typical bullet.
  3. Simply a higher power rifle cartridge necked down to an intermediate one. This would be something like 7.62 NATO necked down to 5.56 NATO. Would heighten speeds, although I'm not sure of the efficiency.
  4. A plasma wreathed bullet. This is a unique one, essentially being a bullet covered in plasma held in place likely by fields emitted by the bullet. Not sure if it realistically works, and even so would probably be expensive.

Essentially in this post, I'm looking for if anyone has any possible solutions to the issues I've seen in what I've already suggested, or has ideas of themselves. The following parameters are:

  1. Must be capable of penetrating high level body armor, preferably also doing some sort of decent damage to who or what it hits.
  2. Must be at least semi-realistic, some slight handwaving is allowed, but no use of fictional materials..
  3. Must be possible to be carried by typically infantry, probably equipped with an exoskeleton.
  4. Preferably sticking away from lasers, but this doesn't mean it has to be a conventional bullet. Feel free to think outside the box, like heat based weaponry or other.

I also realize I might be looking in the wrong place, and the answer might be in more effective recoil dampening systems, or by using weapons that don't rely only on penetration and instead brunt force. Another clarification is that it doesn't necessarily have to be built to penetrate that armor, instead being more general for just high penetration, I was more just introducing the situation and why I need it. Regardless, thanks for the help!

  • $\begingroup$ You haven't said what the RHAe equivalent (en.wikipedia.org/wiki/Rolled_homogeneous_armour#Current_use) or any other physical characteristics of your hypothetical body armor is so the question is not really answerable. Nevertheless, if the soldiers have a powered exoskeleton to handle the weight, a possible option is plain old armor piercing .50 BMG rounds from a heavy machine gun. Depending on the specific type of AP round used, penetration can be up to 16-25 mm of steel armor, which is much more than this hypothetical body armor is likely to be able to handle. $\endgroup$ Jun 3, 2021 at 3:00
  • $\begingroup$ @GrumpyYoungMan RHA generally isn't used when it comes to body armor, as far as I'm aware, and I did give a a round to be compared, so I didn't really think much more would be needed. Regardless, what I'm mostly asking for is just viable options for rounds with high penetration power. As for your .50 BMG suggestion, even with an exoskeleton that is... fairly unrealistic to be shoulder firing in a non-prone position. Also, clarified a bit in the post. $\endgroup$ Jun 3, 2021 at 3:13
  • 1
    $\begingroup$ Is penetration absolutely necessary? Look at the following m.youtube.com/watch?v=cxyJRGxWN0k from 7m45s. Body armor might prevent the penetration, but it won't protect you. As one comment points out: "Its the difference between an open or closed casket". You only need a certain power and it's always effective. $\endgroup$
    – Trioxidane
    Jun 3, 2021 at 5:38
  • $\begingroup$ "capable of stopping most body armors"... Strange phrasing, people don't usually shoot body armors at you. $\endgroup$
    – PcMan
    Jun 3, 2021 at 5:45
  • $\begingroup$ If an armor-piercing .338 Lapua magnum is inadequate, well any railgun, coilgun, squeezebore, necked down rifle cartridge, etc. is going to have recoil at least as bad as that to generate the necessary projectile energy thanks to Newton's third law. And .338 Lapua magnum already has about half the muzzle energy of .50 BMG, so it's not all that manageable as a shoulder fired weapon already. This implies that none of the other possibilities listed in the question realistically work either, other than the gyrojet or "plasma bullet". $\endgroup$ Jun 3, 2021 at 5:48

6 Answers 6


You could always go with HEAT (High Explosive Anti-Tank) munitions. Shaped charge explosives that drive enough material into the interior of whatever is being targeted that survival isn't particularly realistic.

Really, it doesn't matter how good armor gets, it is always possible to bring a bigger boom.

  • $\begingroup$ I upvoted as a shaped charge was also my first idea when reading the question, but it won't work because of human rights. Explosive ammo is banned, because it creates unnecessary suffering. Still, any two or more stage ammo is probably the best bet for penetration without going full scifi. $\endgroup$
    – Trioxidane
    Jun 3, 2021 at 6:53

Grenade launcher

  • Usually only the torso is covered by body armor, shrapnel will still hit the unarmored parts of the target
  • The concussion can still fatally injure the target since the shockwave simply passes through the armor without breaching it, injuring internal organs

Multi-shot grenade launchers such as the Milkor M32 exist and the exoskeleton can help with managing the weight of the ammunition and possibly assist with aiming.


Frame challenge

You state that your body armour will protect the wearer against powerful firearms and lasers. You then ask for a powerful firearm which will defeat the purpose.

Unless I've drastically misunderstood, your premise contradicts your desired result.

Exotic solutions

So, if we say that "armour" beats "normal", then "exotic" beats "armour". Your armour is made of "technobabblite" which is resistant to penetration and impact, and actively cooled. How can we damage a so-protected creature?

First, target the squishy human. Humans don't do so well with sudden acceleration, pressure shocks, radiation, or corrosives. Another answer mentioned concussion weapons, so we'll leave those weaknesses aside. We will consider why everyone doesn't use "exotic" ammo normally.

Radiation: Polonium-coated explosive bullets, to hit any chink in the armour. One scratch is a kill, with a delay shaped like an illness.

Corrosives: These don't work immediately, but render the armour useless for later fights. (And possibly require the wearer to remove it, if the corrosive can get inside from later shots.)

Magnetism: Superconductors can be "charged" with a strong magnetic/electrical field ahead of time, which flows with no loss or resistance. When the superconductor breaks/warms, there's suddenly a lot of resistance. With clever design (handwaving), this could put a lightning bolt through your target's armour.

Antimatter: Superconducting magnetic bottle + impact = bright flash. Very bright. Do not drop this ammunition.

Nanites: If it can build it up, it can take it down. Power them with tuned-frequency light, if you want to avoid a grey-goo scenario.


Needle ammo

Viva la weird. The ammo you're using needs to get as much energy from the bullet past the body armor. So lets do that with needle ammo! This is much like tranquilizer darts, but for gun use. The bullet is normal shaped with a needle in front. On a head on impact the needle can penetrate because of it's tiny surface area. The moment the "normal" bullet tip hits the armor it'll deform, coming to a standstill. The force of the liquid inside the bullet will continue, forcing a lot through the needle and into the body, where it'll expend every bit of energy. Though some energy is lost on the body armor, you'll have a high energy expanding liquid inside the body doing damage. In essence some of the bullet enters the body like this.

So much like a tranquilizer bullet, the force of impact, together with inertia of the liquid, will force liquid through the hollow needle into the body.

"But won't only a head on collision work with the needle?"

This is certainly true, but it'll act like a normal bullet when at an angle. It'll deflect, doing minimal damage. So you're not giving up anything. Well, except for some relatively complex bullets, magazines and loading mechanisms.

  • $\begingroup$ I’m confused, how does the bullet work? Is the liquid forcing the needle out of the gun or is it forcing it’s way out of the needle? If it’s the latter wouldn’t it just spill out if the bullet was jostled around when in the magazine or something? $\endgroup$ Jun 3, 2021 at 7:25
  • $\begingroup$ @ZoTheCutestPirate if you're asking the question I obviously didn't write it well. Like tranquilizer needles, the impact will force the liquid through the needle. That reduces the need for complex mechanisms to push the liquid into the body. However, even with tranquilizer needles this can already do damage. One shot from a gun can be devastating. $\endgroup$
    – Trioxidane
    Jun 3, 2021 at 7:28
  • $\begingroup$ Oh! I think I understand the idea now. So essentially it’d be like putting a flechette with a small hollow section on the top of a typical bullet. Then, inside of the bullet there’d be... let’s say, mercury. Upon impact, the flechette tip penetrates while the bullet gets stopped. Inside the round, some sort of gas pressure forces the mercury out at fast speeds to mess up the internals of who it hits and probably gives them mercury poisoning too. $\endgroup$ Jun 3, 2021 at 7:39
  • $\begingroup$ @ZoTheCutestPirate exactly. Although water is probably enough for lethal damage and much cheaper. In addition, as the bullet stops the liquid can still move through the needle. It'll keep moving automatically. No gasses or other pressures needed. Just firing the bullet and physics will do the rest. But using Mercury would make the hit anywhere on the body lethal if it penetrates the skin. $\endgroup$
    – Trioxidane
    Jun 3, 2021 at 7:45
  • $\begingroup$ I chose mercury since as you said, it’s more deadly and because it’s denser than water, which helps to give more penetrating power to the bullet. Anyways, the reason I figured a pressure system would be needed is since some force like suction would be needed to keep the liquid from flowing out if the magazine or bullets is jostled around before firing. $\endgroup$ Jun 3, 2021 at 7:51

HESH rounds

This is kind of a combination of 2 previous answers. As described here, HESH rounds are a type of explosive ammunition that conform to the target to transmit the shock wave directly through the surface of the armour into the wearer. It would incapacitate or kill the same way a HE round would, but the more directed detonation should reduce collateral damage while simultaneously being more lethal to the meatbag you need to get rid of.

Weapons using HESH rounds already exist for infantry today. If advanced armour(power armour?) becomes a known threat, it's not a stretch to imagine further development to miniaturise such ammo for grenade launchers

  • $\begingroup$ HESH rounds are actually a very interesting concept and weapon, but the main issue is that the only way I could viably see it working to be carried by typical infantry would be through plastic explosives much more powerful than we have today. $\endgroup$ Jun 9, 2021 at 5:44
  • $\begingroup$ @ZoTheCutestPirate Typical infantry today also don't pack coilguns or plasma wreathed bullets, so an improved explosive formula shouldn't be too much of a stretch. Besides, if you only want to knock out a single person directly under the special armour you don't need that much explosive $\endgroup$ Jun 9, 2021 at 8:48

Anti tank rifles are difficult to handle and have a strong recoil, but they have been there for quite some time. This is an example.


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