What can be used to make the world's deadliest bullet?

Question

In a hypothetical near-future setting, humanity has been subjugated by an upper class of cyborgs. A melding of man and machine, they rule the world with an iron fist. The resistance has one chance to assassinate the supreme leader of the cyborgs, but the only weapon that will fit into the plan is a Mk 14 EBR. (it is the weapon most often employed by the rooftop snipers of the regime, who the assassin will imitate.)

Given modern science (plus anything that could be plausibly extrapolated from modern science), what can be loaded into a 7.62×51mm NATO projectile for maximum lethality? (Up to and including overkill or splash damage. Adjacent targets will be other ranking members of the regime, getting them too is a bonus.)

Assume:

• Everything that modern science has to offer currently or can offer within 10 years.
• No Antimatter
• Radius of the bullet's effect cannot be greater than the effective range of a normal 7.62 chambered rifle. (1000 yards at maximum)
• Money is no object.
• Information is sketchy on what parts of the target are enhanced. Assume the round needs to penetrate both flesh and titanium plate.

Answer 1

There are 3 main things you can use to increase the deadliness of a bullet:

1. Increase the damage it inflicts on impact;
2. Add a secondary effect that gives extra lethality;
3. Increase how many you can fire in a given timespan.

Maximum damage:

Damage can be increased by 3 things:

1. Increase the speed at which it flies. The main problem with that is that the faster the bullet goes, the more likely it is to just punch a hole in the target, which actually reduces the deadliness.
2. Increase the mass of the bullet. This has the same issue as increasing the speed, with the added factor that it will also slow the bullet down.
3. Make the bullet increase in size on impact. This is the infamous hollow-tip bullet, which is designed to desintegrate on impact and shred the muscles and vital organs of the target. This is banned in international warfare by the Hague convention of 1899.

Secondary effect:

again, 3 options:

1. incendiary ammunition. Either it puts the target on fire, inflicting secondary burns, or it explodes on impact. the main problem is that a 7.62 round has very limited space for a payload. to compare: the round itself weighs only 10 grammes of solid metal (140 grains). There are explosives and incendiaries that work on that small scale, but most of them require a special detonation device since they're impact resistant. The upside is that explosives, for the same weight, are vastly more effective at handing over energy. 1 gramme of TNT gives 25% more energy than an entire 7.62 round fired from a Barrett does.
2. toxic ammunition. This introduces a viral, bacterial or chemical payload to the target which can rapidly affect the health of the victim. The main problems here are A) ensuring intact delivery of the payload and B) preventing collateral damage when dealing with contagious payloads.
3. Radioactive ammunition. Ammunition containing small amounts of radioactive material are already in use, primarily as anti-tank weaponry.

More Dakka:

1. More barrels. weapons like Gattling guns and the ITM Model 3 (which already fires 7.62 rounds) have multiple barrels and can fire more bullets at once.
2. Faster trigger mechanism. advances in trigger mechanisms could allow guns to fire bullets at an even higher speed.
3. no barrel. There are currently experimental weapons that have a rotating disk design that can fire spherical bullets at extreme rates. However, these aren't 7.62 rounds anymore.

Multiple targets:

The above methods are aimed at increasing the killing power for a single target. A special design could allow the round to ricochet, hitting multiple targets. This does mean there's a higher chance at collateral.

Accuracy:

The main problem with weapons supporting the 7.62 round is that they aren't extremely accurate. If you fire at a target that's over a few hundred yards away, chances are some bullets won't hit them. A weapon with automatic aim adjustments based on the shot before can increase accuracy. You could even develop a system that can adjust the trajectory of a bullet in-flight, allowing for more accurate shots.

Ditching the bullet:

At a certain speed, it doesn't matter whether what you fire is a 7.62 round or a piece of licorice shaped like a 7.62 round. In fact, you could come up with a weapon that can fire anything. As with the barrelless weapon, this is not a 7.62 round anymore.

Final thoughts:

Keep in mind that our current society has a preference to avoid "dirty" warfare. We rather don't want our projectiles to kill targets other than the one we want, and we don't want our weapons to cause prolonged death struggles. We also don't want our ammunition to deal damage AFTER it hit the target. That's why things like cluster ammunition is banned.

Answer 2

Assuming that we need maximum lethality on an armoured target, with collateral damage being considered highly desirable, the most logical ammunition is a long-rod penetrator. So, we base this ammunition around a 5x~45mm uranium needle (so as to fit inside the 51mm length of the ammunition without fouling on the cartridge's base & primer) with a non-discarding finned jacket filled with 4g of Polonium-210 powder, functionally an APCR/HVAP projectile. We fill the 7x51mm NATO brass with a HNIW-based propellant in order to achieve the maximum muzzle velocity.

We fire this ammunition from a weapon that looks like the required Mk 14 EBR, though we modify the rifle to have a much stronger barrel and to be smoothbore, since long fin-stabilised ammunition is faster and more damaging when not spin-stabilised. We load the brass to the point where mechanical failure of the weapon is possible after a single magazine of these rounds are fired, in order to achieve the maximum muzzle velocity, assuming that the shooter is sufficiently protected against mechanical failure of the weapon, or is a suicide agent.

So, we have several avenues of lethality. We have a cartridge loaded to produce very high muzzle velocities, at the cost of effectively destroying the rifle within a single magazine-worth of shots. We have a jacket filled with Polonium dust, that will be stripped off the depleted-uranium penetrator on impact and will burst, filling the air around the victim with several grams of Polonium-210 dust, which has an LD50 of .089 micrograms The depleted uranium penetrator carries most of the kinetic energy on into the victim, passing through any practical thickness of titanium armour (if any) and most likely disintegrating since uranium is brittle, delivering the remainder of the kinetic energy to the target's vulnerable organic or electronic vitals.

So, we have a cartridge that can literally kill millions, mainly from the Polonium-210, assuming that the Polonium disperses widely enough, and considering that the Polonium is concentrated in a relatively small area, we can assume that - provided the Cyborg leader's fellow regime members breathe - they will die within days, having received a lethal dose of radiation within minutes of inhaling the stuff.

A standard 7.62 NATO M61 AP round can penetrate about 13mm of steel armour at its muzzle velocity of about 840 m/s, and at 2000 m/s, the armour penetration capability of a ~45mm depleted uranium flechette would be much higher, and using Newton's Impact Depth approximation, Depth ~= Length x (Projectile Density/Armour Density), potentially penetrating up to 112mm of steel armour, or 190mm of Titanium.

It is most likely not practical to armour a human-seeming or even a humanoid cyborg with Titanium to a degree that this ammunition would not be able to penetrate, and even if the projectile does not kill the target outright, the Polonium-210 most likely will.

Answer 3

You could build a small flux-compression generator into a bullet, possibly replacing the explosive charge with simply the impact force. That would give you the combined effect of an hollow or explosive round with an electromagnetic pulse which I imagine would be quite good against cyborgs.

Answer 4

Given modern science I think there is plenty that could be done, the issue being how cost effective would it be? I think experimental rounds might venture into replacing the bullet with various types of explosives. Russia had developed fulminating musket balls that were designed to take out powder kegs or other strategic targets. This development led specifically to the "Saint Petersburg Declaration of 1868" which bans the use of explosive and fulminating ammunition weighing at or under 400 grams.

The treaty only really covered "small arms" mainly rifles and pistols larger weapons like artillery are basically exempted from the treaty due to the size of the ammunition they fire.

My next example is based on the 25mm grenade launcher the XM25 which has a range setting function that allows the grenade to explode (air burst) at a preset range dealing damage to targets behind walls, in trenches, or behind hills. I imagine that with some further technological advancements (and miniaturization) this type of technology could easily find its way into bullets instead of small grenades.

Answer 5

The payload can be a ricin-laced projectile (like in the historic KGB killing in Oslo(?) where an umbrella tip was used for delivery of a minuscule metal sphere). There is no cure. You need enough penetrating power to deliver the payload reliably.