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Like many other writers, I'm hoping to create some sort of justification for destroying the monopoly firearms have on the modern combat scene so that I can justify mixing things up with melee weapons, archery, slower-than-bullet magic, etc. I'm hoping to do this by using my story's magic system to knock guns down a peg, and after giving it a lot of thought, I've come up with a solution with potential. But I need to run it past some more knowledgeable people to see if this would actually work.

The gist is that, when the inciting event of the story renders nearly everyone on Earth low-level superhuman and capable of using magic, it also alters how the laws of physics interact with the human body in a few key ways, and one of those is that all solid objects colliding with the human body have an "effective speed limit" proportional to the object's mass, and any velocity beyond that speed limit is completely ignored once the object collides with the person and it's time to "calculate the damage" of the impact. To be clear: this doesn't change how fast objects move. It only changes how fast the human body acts like it's moving when it's struck.

For example, let's say, just to demonstrate the concept and not declaring this as the actual value, that the effective speed limit of an object, in feet per second, is equal to 100M, where M is the object's mass in pounds. This means that a 700 grain (0.1 pound) bullet, when shot from a gun, would only damage the human body it collides with as if it were traveling at 10 feet per second, instead of the staggering thousands of feet per second they usually get. Meanwhile, a sword, which weighs 3 pounds on average and is normally swung at speeds well below the sword's effective speed limit of 300 f/s, would be completely unhindered and be just as effective.

This changes the formula for momentum to p=mv, p(max)= Xm2, where X is the feet per second per pound that the mass-proportional speed limit is set to.

Since an object's mass now also determines its effective velocity, this means that, until an object becomes heavy enough that its effective speed limit exceeds its actual speed, a doubling of the mass of a bullet results in a quadrupling of momentum, which suddenly makes small projectiles much, much, much less viable.

The idea here is to force bullets to be big. Big, cumbersome and slow-loading enough that while they aren't completely nonviable and still have their advantages, guns are no longer the rapid-firing, compact bringers of instant death they were once allowed to be. Ideally, guns will be more like they were in the early days: cumbersome, slow to load, and barely more powerful than archery for the trouble.

I'm fairly certain this would make melee weapons relevant again, but the issue comes to archery. I've been informed of certain facts regarding the comparative weight of the heaviest calibers of bullet and the general weight of arrows. Apparently guns can fire some very, very heavy bullets, as much as 3000 grains, without much issue, and the heaviest bullets drastically outweigh most if not all arrows. While bows would be stronger here than in real life due to humans in my universe having the strength of two men, and thus arrows could be made heavier, this still calls into question whether or not a sweet spot weight even exists that would nerf guns but not render archery physically impossible. I'm willing to accept that in order to use this system I have to give up any prospect of including archery, but I'd like to see if it's still possible to make this work.

Is it possible to set a minimum weight projectiles have to weigh to achieve penetration that is too heavy for bullets to be fired more than once every few seconds, but light enough for arrows to be shot from bows with draw weights of double human strength or less?

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    $\begingroup$ Hi Jason. What you're describing (and would make your question clearer) is momentum. You're saying that the velocity component of the momentum is 'capped', but the mass component is not. Explaining it that way might actually draw more scientific answers. $\endgroup$ – Tim B II Mar 25 at 0:52
  • $\begingroup$ @TimBII Thanks for the advice. I'm a bit confused though: what part should I change, and what would you recommend I rephrase it as? $\endgroup$ – Jason Clyde Mar 25 at 0:55
  • $\begingroup$ The paragraph that starts in bold and has For Example is describing what you're asking, but this could be greatly simplified by saying something like 'the velocity of a 700 grain bullet is capped at 100m/s in terms of momentum, but that's multiplied by the mass (regardless of value) to determine momentum of impact. So, a sledge hammer hitting you at a slower speed but at or above the velocity cap (but weighing a thousand times as much) has a momentum at point of impact of 1000 times, meaning that the speed is taken to be the same'. Something like that. $\endgroup$ – Tim B II Mar 25 at 0:58
  • $\begingroup$ @TimBII Just to be clear, the effective velocity limit is proportional to the mass of the object, not fixed. Heavier objects are allowed to apply more of their velocity to the momentum equation before the excess is ignored. $\endgroup$ – Jason Clyde Mar 25 at 1:00
  • $\begingroup$ Well yes, that's one way to put it, but your math looks differently the way you've expressed it. What your math shows is that mass can be anything, but there is an upper limit to velocity. By using a constant (100), you're effectively putting a limit on speed, meaning that momentum is increased through mass, not velocity past the speed limit of 100 $\endgroup$ – Tim B II Mar 25 at 1:02
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The effect you're describing could at least in part be achieved by greatly increasing the atmospheric pressure of a planet, or even adjusting it so humans live in a liquid without them realising. Yes, this part requires a liberal dose of handwavium sprinkled about, but ultimately the greater the wind or atmospheric resistance, the more lowering the mass of an object is going to have an effect because it's taking the same amount of energy out of every object passing through it at a similar rate, aerodynamics notwithstanding.

This last point is important, because your melee weapons and the like are going to work better if they are thin and sharp, like swords or axes, not hammers. It's also going to work better for arrows, which are heavier but also aerodynamic and therefore more likely to retain as much of their momentum as possible while moving through the thicker air.

Bullets in their current form will suffer, but their current design (blunt lead projectiles) is to maximise damage in an environment where their velocity counts. In this new situation, bullets may well survive as a combat measure, but they'll have two major modifications;

1) Convert to harder metals and a sharp point, and
2) Only be used as high velocity (long range) rounds, think snipers.

The reason for this is that the harder metal and sharper point means that the bullet does more penetrative damage when it hits, maximising what momentum it can still retain, but becomes less lethal in the process. With the exception of head shots, the bullet won't cause as much damage by deforming and spreading the kinetic energy out over a wider impact area, so it's now restricted to a long range wounding weapon in most situations.

Your arrows in this situation will also now have very sharp tips, and will be designed to wound as they currently are. Bullets in this scenario are effectively constrained to being long range arrows, although the arrow is probably in most instances the better and more effective weapon at short and medium range by virtue of its mass.

The real winner out of this will be your melee troops, who will have swords and spears for slashing and wounding across a broader surface area than arrows or bullets which have to keep their contact surfaces constrained as a sacrifice for longer range. Despite this, arrows will continue to be effective as a wounding weapon as it's unlikely that this 'upper bound of momentum' effect will be strong enough to constrain the momentum at impact of the arrow, and a sharp point would actually do more to make the arrow effective in any event.

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See S. M. Stirling's Emberverse, starting with "Dies the Fire". In an instant, all electricity stops, high speed chemical reactions (gunpowder) fizzle, and it's impossible to get useful work with air pressures over about 150 psi.

Interfering with the speed of chemical reactions is a good bet. It would mean that you might be able to make steam powered cannons if you can get high enough pressure steam (thousands of PSI) Guns would be very cumbersome. Mechanical siege weapons would come into play: Trebuchet, mangonel, catapults, as well as both bow and arrow, and slings, atlatls, throwing sticks.

A physical change such as tripling the air pressure, by adding extra argon would allow guns to work, but the velocity drop from air friction would be

As a kid I played LaCrosse. This is a dangerous game played with a rubber ball. (A lacrosse ball is about the same weight and only slightly softer than a baseball hardball) A lacrosse stick, some training, and potato sized rocks could be bad news. A sling is more efficient -- most of the energy is in the stone, where with a throwing stick of any form you have energy in the stick that you have to stop for your next throw. But you can train a peasant in a day to be effective at putting rocks into a massed charge.

This opens the possibility of a "Pedal powered anti-personnel catapult." where some sort of wheel with cups, grooves, etc throws a rock at the enemy. Would require a well balanced wheel and good bearings. Given the relative strength of legs vs arms, I would think you could be about 5-15 times as efficient at transferring energy from your legs to the enemy's armour that arm powered projectile (You still need to concentrate the energy on a small enough area to inflict damage.

With a conventional sling, consider the effect of lead pellets the size of a robin's egg instead of a stone.

A boy's rubber band style wrist rocket slingshot used with 1/2" steel bearings can be deadly

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What you are describing would work. I would simply restate the kinetic energy formula with a Log function on the velocity bit so that it receives a maximum kinetic energy from velocity. This would have massive consequences for much of your world though.

But I think you can do it simpler: introduce runes. A rune would be a minimum size. Armor can be enhanced to be nigh impenetreable and its cheap and easy... But a counter rune is easily made on weapons. Problem is that bullets of sufficient size are so cumbersome and the recoil so great that you are better off using swords and arrows. This also limits what kind of ammo everyone uses, since an artillery shell that explodes also destroys its runes and becomes ineffective unless it hits you directly.

An alternative to runes is that each magic user can use its magic to Block enemy fire. An opponent can bypass this jf he concentrates magic in his weapons... But only if he can actually see and focus on it. High velocity projectiles regrettably are too fast so a slower projectile or melee weapon it is then. Another alternative is that mass is what carries the magical potential, but this magical potential leaks away the moment it leaves proximity with the wearer, the farther away the faster this goes. A bullet has lost almost all its magical potential to penetrate someone's armor while an arrow still has enough to do damage. And melee weapons become even more universally used as they lose no energy and stay close enough to be powered.

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  • $\begingroup$ love the runes. you can even still have anti-materiel rifles (speed limit is only against humans, right?) and guns (you'd be able to charge through a barrage, because the shrapnell won't get you). you could also still have elite snipers (using ultra expensive rune-inlayed bullets). Very cool! $\endgroup$ – bukwyrm Mar 26 at 15:25

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