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Old 01-13-2023, 02:15 PM   #41
Anthony
 
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Default Re: [Ultra Tech] Increased Firearm Power with TL

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Originally Posted by Ulzgoroth View Post
Wait, what exactly would new propellants change about the problem? Going into the future, as per the seeming topic of the thread, not going forwards from black powder.
As your ratio of powder weight to bullet weight increases, more and more energy gets wasted accelerating the powder instead of the bullet -- .220 swift is getting around 40% less bullet energy per gram of powder than .223. Solving that requires using propellants with higher specific energy.
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Old 01-13-2023, 02:21 PM   #42
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Default Re: [Ultra Tech] Increased Firearm Power with TL

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As your ratio of powder weight to bullet weight increases, more and more energy gets wasted accelerating the powder instead of the bullet -- .220 swift is getting around 40% less bullet energy per gram of powder than .223. Solving that requires using propellants with higher specific energy.
Higher specific energy doesn't solve that problem at all, it just makes the increasingly inefficient propellant pile that much lighter.
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Old 01-13-2023, 02:24 PM   #43
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Default Re: [Ultra Tech] Increased Firearm Power with TL

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Originally Posted by Ulzgoroth View Post
Higher specific energy doesn't solve that problem at all, it just makes the increasingly inefficient propellant pile that much lighter.
Part of the efficiency loss is because you need to spend energy to accelerate the powder (as well to accelerate the projectile). The less powder weight you have, the less energy you need to spend accelerating it.
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Old 01-13-2023, 02:40 PM   #44
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Default Re: [Ultra Tech] Increased Firearm Power with TL

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Frankly, we may have hit the limits of solid shelf-stable monopropellants (note that GURPS has REF 4 explosives at TL 9 and REF 6 at 10, which indicates something new, but there's no evidence of anything that dramatic actually occurring).
Are modern small arms using propellants at this limit? I know there has been talk of using high explosives as propellants, but maybe those aren't shelf-stable or are otherwise unfeasible, and we're stuck with modern smokeless. Or maybe there could be a dramatic breakthrough of some flavor.

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This is a kind of odd framing, since adding more propellant, absent carefully changing the nature of that propellant, will extremely directly translate into increased chamber pressure. What you're calling 'more propellant' here seems to be a prolonged burning curve...which does require more propellant, yes, but it doesn't stop there!
My apologies, I skipped a step - it was meant to be read as something like "more propellant gets you better performance but requires a longer barrel if you maintain the same peak pressure" (because your weapon can't handle higher).
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Old 01-13-2023, 03:32 PM   #45
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Default Re: [Ultra Tech] Increased Firearm Power with TL

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Are modern small arms using propellants at this limit? I know there has been talk of using high explosives as propellants, but maybe those aren't shelf-stable or are otherwise unfeasible, and we're stuck with modern smokeless. Or maybe there could be a dramatic breakthrough of some flavor.
The defining characteristic of high explosive is highly undesirable for a propellant, since you don't want to burn near-instantly as a rule. (Of course, if you get more specific energy, maybe there's a justifying trade-off there.
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Old 01-13-2023, 04:45 PM   #46
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Default Re: [Ultra Tech] Increased Firearm Power with TL

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Are modern small arms using propellants at this limit? I know there has been talk of using high explosives as propellants, but maybe those aren't shelf-stable or are otherwise unfeasible, and we're stuck with modern smokeless.
Modern smokeless powder is closely related to high explosives and has similar energy density. One of the motivations for liquid propellant is that there are binary liquids with higher energy densities than exist for monopropellants.
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Old 01-13-2023, 05:02 PM   #47
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Default Re: [Ultra Tech] Increased Firearm Power with TL

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Originally Posted by Ulzgoroth View Post
The defining characteristic of high explosive is highly undesirable for a propellant, since you don't want to burn near-instantly as a rule. (Of course, if you get more specific energy, maybe there's a justifying trade-off there.
I mean, if you're at the point where you can't fit more propellant in the projectile but your weapon could handle a markedly higher chamber pressure, it seems like maybe you could get a boost from a high explosive. It might be interesting if such rounds have a distinctive feel to firing them - the powder burns first, sending the bullet partway down the barrel (giving more room for the high explosive to expand into upon detonation), then the high explosive charge detonates, momentarily peaking out the chamber pressure and giving the projectile a shot of turbo. This would feel like two explosions in rapid succession (because that's what it is), the second much larger than the first. Or maybe that's not really possible, and the high explosive would simply go off as soon as some of the powder does (maybe you could get the powder to keep burning just so the pressure fall-off isn't so high?).

From a brief bit of searching online, it sounds like modern smokeless powders basically have a limit to their REF (and I think specific energy should be roughly proportional to that) as equaling that of nitrocellulose, which HT183 puts at REF 1.3. There are plenty of explosives in HT with higher REF than that, such as CL20 at REF 2.3 (which is also denser than nitrocellulose, so no worries about it taking up more space than a comparable energy of cordite), and I would expect there to be UT explosives with even higher REF (and still good density).
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Old 01-13-2023, 05:40 PM   #48
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Default Re: [Ultra Tech] Increased Firearm Power with TL

It appears some of the interest in CL-20 is for rocket propellant, so it's probably also usable in bullet-propellant.
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Old 01-13-2023, 06:19 PM   #49
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Default Re: [Ultra Tech] Increased Firearm Power with TL

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There are plenty of explosives in HT with higher REF than that, such as CL20 at REF 2.3
I think GURPS uses a somewhat peculiar definition of REF; the figure I find for CL-20 is about 1.9. Current double-base smokeless powders are already a mix of nitrocellulose (1.1) and nitroglycerine (1.54) and I see discussion of use of RDX (1.6). You don't see any of the more energetic compounds in pure form, they need things to moderate their burn rate and stability.

So.. there may be room for incremental improvement, but there's just no real evidence for anything dramatic, RDX dates from 1894, HMX from 1930.
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Old 01-13-2023, 11:50 PM   #50
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Default Re: [Ultra Tech] Increased Firearm Power with TL

Another possibility is not more or faster- or hotter-burning propellant, but more efficiently-burning propellant.

For example, modern "black powder" guns are more efficient than their TL4-5 predecessors because grains of black powder substitutes like Pyrodox are uniformly sized and are shaped for optimum combustion. That means more combusted powder and less wasted material going out the muzzle or fouling the gun.

If you had carefully designed layers of powder in a cartridge designed so the initial fast-burning but not-so-hot particles closest to the primer subsequently ignited layers of slightly slower-burning but hotter particles as the bullet goes down the barrel, you could get the same or better muzzle velocity with a smaller powder charge.

Extending the primer down the center of the cartridge to alter combustion dynamics might also make for a "hotter" round while using the same amount of powder.

Figuring out precise combustion mechanics for interior ballistics on a molecular level is currently close to guesswork. Supercomputer modeling which optimizes combustion energy would be entirely reasonable at higher TL even if you don't have super new propellants.

Mixing in layers of very fast-burning, very hot material, like a tiny bit of high explosive, at the very end of the burn might give bullets an even greater kick without blowing up the gun.

The drawbacks might be that cartridges would have to be matched to not just weapon caliber and chamber length but also barrel length in order to get optimal performance. Barrels might also have to be redesigned to cope with progressively higher rather than lower interior pressures as the bullet moves towards the muzzle.
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