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PostPosted: Fri Feb 24, 2012 12:22 am 
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A little background:

Tonight, I was running my TNE-derived game, and the players were once again in a position where they didn't have access to their gosh-wow firearms, so were forced to make do with black powder weapons and a discussion about how they were "survival weapons" and so on with low-tech requirements.

However, as the GM, I began to wonder: "is this the best we can do for a survival rifle?" Black powder is a bit of a pain to make: you need charcoal, sulfur, and saltpeter any of which may be problematic on many worlds.

So I started to wonder if it might be possible to make a "survival" rifle that works better. A survival rifle in this case would mean it would have be durable, very low maintenance, and easy to use. The weapon would have be capable of extended neglect and still function. As it requires little or no user maintenance, it could be made at a high TL but be useful for anyone who could be taught the weapon's operation.

Leaving aside really high-tech options (like the grav-powered rifle), my first idea was for a solar-powered laser rifle. Contain the solar panels in the buttstock of the weapon under a durable, transparent cover. It'd be a microsecond pulse laser design (designed to do damage by rapid heating). It's attractive because it seems that it could be made pretty much solid-state.

The Actual Question:

While the laser rifle was pretty interesting (I may still go with it), I began to wonder about the viability of a rifle that uses the oxygen-hydrogen reaction as a propellant. It'd still have the solar-powered system and perhaps an agitation system (like a self-winding clock) to power the rifle. The rifle would require a water supply (filtered by a simple high-tech micropore filter). The hydrogen and oxygen would be split and stored in separate reservoirs, good for a few shots. When the trigger is pulled a "squirt" of hydrogen and oxygen into the chamber. The reaction would push the bullet out of the chamber.

Leaving aside all that, I'm curious if a hydrogen-oxygen reaction would actually work as a propellant for shots? Does it have enough impulse? Too much?


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PostPosted: Fri Feb 24, 2012 12:49 am 
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epicenter wrote:
While the laser rifle was pretty interesting (I may still go with it), I began to wonder about the viability of a rifle that uses the oxygen-hydrogen reaction as a propellant. It'd still have the solar-powered system and perhaps an agitation system (like a self-winding clock) to power the rifle. The rifle would require a water supply (filtered by a simple high-tech micropore filter). The hydrogen and oxygen would be split and stored in separate reservoirs, good for a few shots. When the trigger is pulled a "squirt" of hydrogen and oxygen into the chamber. The reaction would push the bullet out of the chamber.

I suspect you would get a better result with a multi stroke pneumatic air
rifle, probably even with a good crossbow.


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PostPosted: Fri Feb 24, 2012 1:11 am 
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epicenter wrote:
Leaving aside all that, I'm curious if a hydrogen-oxygen reaction would actually work as a propellant for shots? Does it have enough impulse? Too much?

Yes, it would work fine. The problem would be with storing the hydrogen. In the first place it takes up a lot of room per unit of energy stored. In the second it diffuses like crazy through seals and valves.

If you want a weapon that stores solar energy, I suggest that high-tech rechargeable batteries will store more in the form factor of a rifle, and will hold a charge better than a pressurised chamber will hold hydrogen. Either a coil gun or a rail gun is solid-state with no moving parts and ought to be very durable. A rail gun might be a little bit fussy about ammo: depending on how the tech to prevent rail erosion works out it might fire anything conducting or it might need superconducting sabots, but either way it might need projectiles moulded or machined to close tolerances. A coil gun is not as simple, and will probably be more expensive, but it ought to fire anything that is ferromagnetic (iron scrap) and will fit down the bore.

Anyhow, suppose that the stock and forearm of a rifle give you 0.03 square metres of solar collector, 50% efficient. In full Earthlike sunshine it will recharge at about 30 W, which is to say collect enough energy to produce the muzzle energy of a 5.56mm NATO round in about an hour, assuming very high efficiency in the weapon part. In a spaceship, in the trunk of an air/raft, in a cave, in a forest or swamp, indoors, in cloudy weather, or on the world of an M-type, K-type, or late G-type star it will recharge significantly slower.

For a practical survival gun I recommend a powerful air rifle made of high-tech materials.

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PostPosted: Fri Feb 24, 2012 1:56 pm 
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I might even go with a Pistol version of your solar powered laser.

The pistol butt sits on your hip, absorbing light all the time, is small and out of the way and "always there". Probably only good for a couple of shots, but it could be used for hunting or to get out of a tight spot.

Pistols would be much easier to carry...

I like the idea though.

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PostPosted: Fri Feb 24, 2012 3:57 pm 
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One could have solar cloth that you unfold and plug into a laser rifle, you could even carry it over your shoulder unfolded to recharge the rifle.

IIRC, nitrocellulose, and other chemical compounds, is easier to make than making a breech capable of holding the pressure. A hydrogen gun would suffer from what others have stated, diffusion in storage most importantly.

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PostPosted: Fri Feb 24, 2012 4:59 pm 
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Frankly, I am not convinced that a solar powered survival weapon
really is a good idea, mainly because I can imagine too many situ-
ations where one would want to have a functioning weapon, but
would have very little sunlight to power it - even a dense forest
or jungle could make such a weapon almost useless, not to men-
tion something like a crash on the dark side of a tidally locked pla-
net ...


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PostPosted: Fri Feb 24, 2012 5:54 pm 
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Cyborg IM1 wrote:
I might even go with a Pistol version of your solar powered laser.

The pistol butt sits on your hip, absorbing light all the time, is small and out of the way and "always there". Probably only good for a couple of shots, but it could be used for hunting or to get out of a tight spot.

Pistols would be much easier to carry...

Yes, but a lot harder to shoot with. Something like an AR-7 survival rifle weighs only two-and-a-half pounds, and gives you rifle accuracy.

I'm still worried about the fact that bright sunlight to charge the thing is not available in a lot of situations, including forests, swamps, cloudy weather, high latitudes, and the planets of cool stars. And now that you are talking about reducing the solar collector area to the butt of a pistol I am seriously concerned about slow recharge times. A pistol butt will give you only about 0.005 m-2 of collector area, which means recharging at only 5W at 100% efficiency perfectly oriented in full sunlight. In real conditions, allowing for reasonable efficiencies, it is going to recharge slowly.

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© My posts to this board are copyright under the Berne Convention. They may be quoted on the board with appropriate attribution. They may not be reproduced beyond the board except with explicit permission from me.


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PostPosted: Fri Feb 24, 2012 6:50 pm 
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I agree with rust about the air rifle. Lewis and Clark took a Girandoni (SP?) air rifle with them on their 1803 - 1806 exploration trip. The rifle produced 800 psi and was able to bring down deer and plenty of small game for the group. It was used to supply food for the team because it was extremely quiet and they often didn't want the local Indians to know they were around.

Dave


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PostPosted: Sat Feb 25, 2012 8:24 pm 
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Air rifle does seem to be the way to go. I'm not too thrilled about the AR-7 as a concept - while .22 LR is an effective round for its size, it seems only good to shoot at other people and small animals like squirrels. Given the variety of biospheres a traveller is likely to encounter, I'm thinking the rifle should be powerful enough to take down a bear - perhaps not in one shot, but at least before requiring reloading/recharging (assuming a reasonably accurate rifleman). However, it'd appear that even early air rifles were able to take down game like deer. It doesn't seem like much of a stretch that a high-tech one might be able to take down a bear.

Also, the idea that solar power wouldn't be enough for a survival weapons is a problem I've considered. I did consider various methods of increasing the solar reception area, but a separate panel of any kind seems like it'd be prone to being misplaced or lost. I'd even been considering the idea that the rifle probably would be able to shoot improvised or low-tech ammunition (with a certain loss in performance) as precision rifle ammunition may not be available.

For a while I was considering some sort of built-in methane-fuel cell for power. Methane isn't hard to get - human wastes produce the precusors for methane. However, the idea that you're using human wastes to power a weapon would probably encounter a certain ... cultural ... resistance, even if the system were relatively fullproof. Methane isn't the most energetic of fuels, but idea of the survival rifle is that it shouldn't need to be shot too many times in a day.

The other ideas was some sort of agitation or kinetic energy generation, like a self-winding watch. A person carrying such a rifle is likely to have it in a vehicle or on their person as they move about, and this constant motion would be used to recharge the rifle over time. The concerns with such a system is that system might have a low power generation rate and, of course, the person using the rifle might not move around that much (perhaps they are injured).

Of course, I guess some sort of system like a hand-crank might work as well to generate electricity. While it doesn't seem elegant (the past ideas were that the user didn't have to take an active role in recharging the rifle), I'm sure it'd be effective, with the drawbacks of the winch mechanism being vulnerable to damage and the handle being misplaced.


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PostPosted: Sun Feb 26, 2012 1:29 pm 
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epicenter wrote:
Air rifle does seem to be the way to go. I'm not too thrilled about the AR-7 as a concept -

I mentioned it only as an illustration that you can get a weapon with the ergonomics and particularly the sight radius of a rifle and the weight of a pistol. It is a real actual survival rifle.

Remember that we are talking about a survival rifle, which is to say something of which the chief virtue is that it is light and compact enough that people can and will carry it in circumstances when they don't expect to need a rifle, small and robust enough that you can and people will stow it out of the way in their trunk, in the back of their passenger cab, in their boat, in their light aircraft…. It is for hunting small game in a survival situation, not for serious self-defence. The AR-7 is an actual success in that role. If you are in a situation in which there is a significant chance or needing to defend yourself—e.g. trucking through bear country—it is wise and usual to pack a heavy pistol, a full-bore rifle, or both.

A survival rifle is to a proper weapon what a survival kit is to a backpack full of supplies and camping gear.

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— Brett Evill

My SFRPG setting, Flat Black

© My posts to this board are copyright under the Berne Convention. They may be quoted on the board with appropriate attribution. They may not be reproduced beyond the board except with explicit permission from me.


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