Solid rocket propellants seem to have a much a higher energy density than smokeless powders. If you could somehow rig a mass of solid rocket fuel to burn almost instantly, would you get higher performance than an equivalent smokeless powder charge? if not, if you disregard safety, what are other potential exotic firearm propellants that may have higher energies?
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$\begingroup$ We have been using gunpowder for centuries for a very particular reason. I don’t remember exactly but I’m pretty sure it has something to due with having the gun not explode in your hands. $\endgroup$– NuclearWillCommented Sep 21, 2021 at 12:58
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1$\begingroup$ you may want to take a look at high explosives. but you may run the risk of the tool explode in your face with those. $\endgroup$– Postlim FortCommented Sep 21, 2021 at 12:59
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2$\begingroup$ What is wrong with taking more gun powder if you need a more powerfull shot? I mean what is the difference which is important for you, between gun powder and propelant. Also a little bit curious where you get it that solid rocket fuel significantly more energy dense than a gunpowder? If we talk about not black gunpowder. Double-base (DB) propellants in in here en.m.wikipedia.org/wiki/Solid-propellant_rocket is basically your typical gunpowder mixed with good old explosives they are equivalent. High performance wiki says it +14-20 percent boost, or you have some other numbers? $\endgroup$– MolbOrgCommented Sep 21, 2021 at 13:38
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3$\begingroup$ Gunpowders are typically used in granular or flake form to increase the surface area and allow faster burning. This unavoidably also increases void space and decreases overall density. The volumetric energy density difference may not be that great when you take this into account. Also, solid rocket propellants aren't formulated to keep gun barrels in good shape. Their energy density comes in part from things like aluminum powder, which burns to produce aluminum oxide, a very good abrasive and something you very much don't want in your gun barrel. $\endgroup$– Christopher James HuffCommented Sep 21, 2021 at 14:15
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2$\begingroup$ Also, as @MolbOrg indicates, typical guns aren't limited by the gunpowder that can be used per shot. They use the amount needed to achieve the desired result, within the limits of what the gun can safely handle. There's considerations of material strength, weight, recoil, etc that you need to deal with before a tremendously higher energy density propellant makes a real difference. $\endgroup$– Christopher James HuffCommented Sep 21, 2021 at 14:22
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2 Answers
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It is a balancing act
It is better to lessen the mass of the projectile. Here, tungsten subcalibre 7.62mm ammunition (image source)
Selecting what to use for propellant, and how much, is a balancing act between getting sufficient "bang for the buck", and not RUD:ing the weapon.
Yes, you are right in that — if we could just cram more energy into that closed space — we could get more energy in the projectile at the muzzle.
The problem is — that in order to hold this energy inside in a controlled manner — your weapon needs to be beefed up, because otherwise it will fail on you. Something as simple as a flawed charge in a .50 caliber cartridge, can have disastrous consequences.
Hence, where weapon technology is today, it is not that we could not use more energetic propellants — there are plenty of those — but we simply do not want to, because then we have to strengthen up the weapons to such a point that they become unwieldy.
Instead, we go the other way, that for a given weapon, we reduce the size of the projectile — i.e. subcalibre ammunition, "darts" — giving it less mass and thus — with equal momentum and roughly the same chamber pressure — we get a better muzzle energy, since momentum depends on speed but inertia on the square of the speed.
For example:
A 50% reduction of mass gives a 100% increase in muzzle velocity (*) for the same momentum, and a 100% increase in muzzle energy.
The higher muzzle speed also affords other advantages, such as reduced flight time, a flatter trajectory and — with that — easier aiming and longer reach.
Then you also have considerations such as...
- Reliability
- Deterioration over time
- Sensitivity to accidental discharge
- Speed of combustion (too fast = massive stress on the gun, too slow = projectile leaves the gun before it finishes)
...and you find that this balancing act is quickly turning overwhelming, and there are way many more issues to deal with than just getting the biggest boom.
So, could we?
Yes, but then we get disadvantages that offset any possible advantages.
(*) Theoretically, no other factors considered. In real life, you will not get that kind of improvement because of things like the propellant gasses not being able to cram themselves into and through the barrel as efficiently.
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$\begingroup$ Muzzle energy is function of charge, soo there is a limit. 0.5 mass gets you no more than sqrt(2)x velocity. $\endgroup$– MolbOrgCommented Sep 21, 2021 at 16:16
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$\begingroup$ WRT speed of combustion, consider what happens to a rifle if you reload using a fast-burning pistol powder: bulletin.accurateshooter.com/2015/01/… (One example of many.) You want your propellant to burn at a controlled rate, depending on the length of your barrel. $\endgroup$– jamesqfCommented Sep 21, 2021 at 16:26
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Flour Power:
The Mill City Museum in Minneapolis celebrates our flour milling history, but it's pegged as the most explosive museum in the world. Why? Flammable materials, ground finely and aerosolized, are incredibly explosive! Flour is 70 times more explosive than gunpowder. The original flour mill on the site vaporized, along with much of what was Minneapolis at the time, in a massive explosion in 1878.
The problem is getting the stuff to behave reproducibly. You need to get a solid to burst into a cloud of particles mixed well with oxygen and ignite it. Flour is more sensitive to moisture and more prone to clumping. You need to introduce an external source of oxygen, as opposed to gunpowder, which contains it's own oxidizer.
But the same principles of thermobaric explosives can be applied to other flammables. The air-fuel bomb is a classic example, where a vapor or droplet-based cloud is ignited to create a massive shockwave. If you really want your solid rocket fuel to give a bigger bang, bursting it as a fine powder mixed with air will give you a really BIG bang. But it might be a really dangerous approach.
