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2010-01-20, 09:28 PM (ISO 8601)
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Re: Got a Real-World Weapon or Armor Question? Mk. VI
Heh. Just kind of an aside . . .
1. Railgun is an interesting term. Historically it referred to massive Naval cannon (Gun), mounted on a Railroad carriage! I was just thinking about how many terms like that have multiple (and usually rather different) meanings. Another one is "needle-gun".
2. Why would you want a railgun (and I assume you are referring to something that propels projectiles using electro-magentism) in space? What benefit would it have?
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2010-01-20, 10:33 PM (ISO 8601)
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Re: Got a Real-World Weapon or Armor Question? Mk. VI
There was a short run pistol which fired a self propelled projectile (essentially a rocket) mentioned in one of this threads previous incarnations. I suspect it would see a resurgence (suitably modernized) if infantry combat in space becomes a necessity.
Found it - Gyro Rocket Pistol - It has issues as is, but brings up interesting possibilities from a gaming point of view...
@fusilier's #2 - Surely Newton's Laws don't apply in space!Last edited by Raum; 2010-01-20 at 10:34 PM.
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I laugh at myself first, before anyone else can.
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The more labels you have for yourself, the dumber they make you.
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2010-01-20, 11:56 PM (ISO 8601)
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Re: Got a Real-World Weapon or Armor Question? Mk. VI
Speaking of guns in space, anyone here ever see the Sean Connery film Outland?
G.
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2010-01-21, 12:37 AM (ISO 8601)
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Re: Got a Real-World Weapon or Armor Question? Mk. VI
Yes. When you fire a rifle, you don't just move the projectile, but also everything in the barrel. Up here where theres air, that's no problem since it's light and it compresses very well. Under water, the tales entirely different. Now you're trying to move a couple of feet of heavy noncompressing water. Depending on how heavily build the gun is, the water may just present more of an obstacle than the bolt, chamnber and barrel, and so the weakest part either crack or goes flying.
In the long term, yeah you'll have problems since the water ruins the oils lubricating abilities.
In the short tems, you might have a problem with whatever reloading system the gun uses, since the water soaks up a lot of power when the parts move through the water.
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2010-01-21, 01:40 AM (ISO 8601)
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Re: Got a Real-World Weapon or Armor Question? Mk. VI
Yeah, as I recall, if you stuck your finger over the "barrel" you could stop the rocket . . . it just accelerated that slowly.
There are various forms of recoilless guns, they're usually big and/or complicated. I think the typical kind, used in bazooka like weapons, blows a jet of air out of the back. This requires more propellant to be used to get the same velocity. I think there were also designs which had a heavy weight that is propelled backward when the gun is fired. The weight is contained, but would have to be reset (and I imagine that this system would also require more propellant). I'm not sure how well it worked. There is some information on wikipedia about the first type, but I can't find out anything about the second kind . . .
I think you anticipated where I was going with this question. Yes, a rail gun is accelerating a projectile forwards using an electro-magnetic force . . . at the same time the gun itself is trying propel itself backward, by pushing off the projectile with the same electro-magnetic force. ;-) That's the clearest way I could think of expressing it.
A lot of things in physics actually defy intuition. That's something I learned about Aristotle's physics. He got a lot of stuff wrong, but he was popular because his physics were pretty intuitive (and there wasn't any way to test most of the stuff, and most philosophers never really considered performing experiments).
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2010-01-21, 02:37 AM (ISO 8601)
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Re: Got a Real-World Weapon or Armor Question? Mk. VI
Railguns have huge advantages over chemical propellant guns in space for several reasons.
1) Logistics. The propellant probably has to be shipped up the gravity well.
The railgun needs magnetic projectiles and power. Both fairly easy to acquirre in space.
2) Polution. If u r using the weapon inside your eco-systym burning propellants polutes your airsystem. Unnessasary strain of the airfilter system is a bad idea.
Externally Railguns can produce higher velocities, which is also a major advantage for shooting at range and for delivering greater KE to the target for the same recoil. Minimising recoil been a big deal as noted.
Stephen E
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2010-01-21, 03:26 AM (ISO 8601)
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Re: Got a Real-World Weapon or Armor Question? Mk. VI
Why? I'm trying to figure out how they can produce higher velocities with the same amount of recoil? (Which implies that they can produce the same velocity with less recoil). I don't know why the recoil forces would be different, unless, perhaps due to inefficiencies in guns (e.g. powder still burning once the bullet has left the barrel, or windage). Not only can those be engineered around to a certain extent, but how significant would those inefficiencies be in a personal weapon?
As far as everything else goes, as you said you have to supply railguns with an external power source. I can certainly see that working for a very big piece of artillery, but not too likely for a personal weapon in the near future. And lets face it, bullets are relatively cheap and light for the power they pack.
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2010-01-21, 05:49 AM (ISO 8601)
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Re: Got a Real-World Weapon or Armor Question? Mk. VI
Recoil is caused by conservation of momentum.
Momentum = M x V
Kinetic Energy = 1/2 M x V(sq)
So if u reduce the mass and increase the velocity the recoil will remain the same, but the kinetic energy will vastly increased.
As a side note in physical combat in 0-gee the velocity of your blows becomes more important. The fast jab is more effective than a slower more powerful blow, due to the effects of inertia.
Stephen E
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2010-01-21, 06:16 AM (ISO 8601)
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Re: Got a Real-World Weapon or Armor Question? Mk. VI
Railguns do not have a volume of propellant gasses that will need to be dispersed- the same way that most muzzle brakes (some do vent the gas backwards) reduce the recoil of the weapon firing them.
Coilguns are a much more practical idea than railguns for personal use- as you can already assemble on your own a coilgun that is as effective as a pellet gun or even a .22 if you've got good components. Militarizing them is a lot more reasonable than militarizing and then miniaturizing railguns.
As far as I can see, the key advantage is that the ammunition is inert, and does not contain a primer than can be set off or propellant that can detonate when heated. From a security standpoint, it's easier to control access to firearms than bullets, and while it's clear that a single malcontent has the ability to kill everyone onboard a space vessel, the concern of someone simply doing something stupid with a bullet should not be dismissed out of hand.
Edit:
Also, a coilgun with a rifled barrel can properly be called a Gauss rifle. This is reason enough.Last edited by Zincorium; 2010-01-21 at 06:18 AM.
"It does me no injury for my neighbor to say there are twenty gods or no god. It neither picks my pocket nor breaks my leg."
- Thomas Jefferson
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2010-01-21, 02:02 PM (ISO 8601)
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Re: Got a Real-World Weapon or Armor Question? Mk. VI
Ah, I didn't realize you were changing the mass of the projectile. So there are, realistically, limits to gunpowder that will prevent you from simply ramping up the velocity, while decreasing the mass of the projectile. I believe this has to do primarily with burn rates. There are also other considerations, than simply increasing the kinetic energy. In terms of armor penetration, I know that materials and shapes, and other more complicated things can come into play. I don't actually know how all those factors work scientifically. Thanks for the clarification.
@Zincorium
As far as ammunition being inert, I would imagine that you have to keep some pretty serious electric charges hanging around to repeatedly use an electro-magnetic gun. High-voltage or amperage batteries aren't usually the safest things around. (My knowledge of electro-magnetism is a bit rusty: to quickly accelerate some mass, would you need both high amps and volts?) Probably have to charge up a fairly serious capacitor too. I suspect that a lot of this stuff is kind of leaky (e.g. batteries lose charge). Meanwhile, all of this high-powered electrical equipment waiting to discharge at a moment's notice is sitting comfortably on your person. I'm not saying that these dangers couldn't be engineered around. Or that loading yourself with a bunch of explosives (i.e. ammunition) is any safer. However, a lot of the dangers of gunpowder weapons have already been addressed.
Although, with an electro-magnetic gun, you do have the benefit of "powering down"; draining the electricity out of the system, so that it's not longer a threat, unlike a cash of ammunition. On the other hand, you have to charge the entire system up again before use. If you wanted to do so quickly, you would probably need to have some big electrical system that could rapidly charge a battery -- which could be almost as dangerous as a cash of ammunition. Although if significant electric power generation is available (foreseeable on a space ship), then such electrical systems would already be in place.Last edited by fusilier; 2010-01-21 at 02:21 PM.
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2010-01-21, 02:33 PM (ISO 8601)
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Re: Got a Real-World Weapon or Armor Question? Mk. VI
But even for a projectile of the same velocity and mass, the railgun will have marginally less recoil because you need to add the mass of the propellant to the equation for a chemically powered firearm.
My primary question is, though, do the heat production drawbacks of a railgun outweigh its advantages over chemically propelled projectiles (including rockets)?
I am not sure that they don't.Last edited by Norsesmithy; 2010-01-21 at 02:39 PM.
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2010-01-21, 04:06 PM (ISO 8601)
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Re: Got a Real-World Weapon or Armor Question? Mk. VI
Ah, good point. However, another question is then presented: Is the added mass significant (you even said it's marginal)? I'm sure that varies depending upon the application, but the point remains that both weapons have significant recoil, which needs to be addressed.
Certainly if a weapon generates a lot of excess heat (which is wasted energy), that's a concern. Especially if you wish to be able to fire the weapon rapidly. I wonder about power generation and storage too.
I just realized something. Cooling in space can't be too simple. Isn't vacuum a good insulator (e.g. a thermos)? Now I have to do some research . . .
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2010-01-21, 04:21 PM (ISO 8601)
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Re: Got a Real-World Weapon or Armor Question? Mk. VI
Trying to answer my own question. I knew it would have something to do with thermal radiation . . . I just don't know exactly how quickly such radiation would take place, and I'm pretty sure it's dependent on the materials. In the vacuum of space, it may be possible to cool down something like a rail/coil gun fairly quickly, if the right materials are used.
I guess like most technology, this is all pretty complicated. :-)
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2010-01-21, 06:27 PM (ISO 8601)
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Re: Got a Real-World Weapon or Armor Question? Mk. VI
Cooling in space is a very big problem, since there's no medium to transfer it to.
This is going to be a big problem for rail and coil guns since they get hot enough that a fairly small number of shots will wear the barrel (Be it rails or coils) away, when fired in an atmosphere. In vacuum that's only going to get worse.
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2010-01-21, 08:42 PM (ISO 8601)
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Re: Got a Real-World Weapon or Armor Question? Mk. VI
I'm not aware of any inherent reason for a Railgun to produce lots of heat.
Putting large currents through wiring can produce heat due to resistance, but if u use superconductors, and why wouldn't you after forking out the money to get all this stuff into space anyway, resistance is negligble and thus heat buildup is low as well.
Railguns will still have recoil of course. Just less for the same effectiveness.
I am making the assumption that u aren't intending them as close range portable firearms, where they have other problems.
Lasers are the way around recoil, having no appreciable recoil unless you get into truly massive power levels. Lasers have their own set of advantages and disadvantages.
Stephen E
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2010-01-21, 10:36 PM (ISO 8601)
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Re: Got a Real-World Weapon or Armor Question? Mk. VI
The used propellant gas is being forced out in a specific direction at high velocity. Not marginal.
Additionally, with a large mass of a gun, combined with a recoiling mount similar to what is already in use for large guns, recoil will not be an issue.
Cooling, in vacuum, is best accomplished by a coolant of some sort that absorbs the heat by expanding. We kinda already know how to do this. Worst case scenario, you can radiate the heat into space with sufficient cooling sinks.
Rail guns get hot due to friction- this is a problem even in atmosphere, because we haven't figured out how to propel it without contact (which will be 100% necessary for military use). Coil guns do not allow the coils to touch the projectile- it may touch a barrel for increased control, but as there is no hot propellant gas and the barrel to projectile fit isn't as tight, it will not heat up to anywhere near what a conventional gun will.
Power density is still an issue to be considered, but we can use the operating current of the space shuttle to recharge supercapacitors that then provide the needed electricity for several shots. Very safe, and only a few years off.
TL; DR:
We have, or will have, solutions to all these problems.
For orbital weapons, we won't use any of these things anyway. Simply sending a piece of solid steel at orbital velocities towards the target is actually overkill."It does me no injury for my neighbor to say there are twenty gods or no god. It neither picks my pocket nor breaks my leg."
- Thomas Jefferson
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2010-01-21, 10:43 PM (ISO 8601)
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Re: Got a Real-World Weapon or Armor Question? Mk. VI
Yeah. Melee in microgravity is just not on. You'd need very special training to do it properly, and even then there'd be a lot of weird risks involved.
Yes, but you've just nailed your feet to the floor. Not good if the other guy has any kind of ranged weapon. Or if they can strike up with enough force to overcome the attraction of your magnetic boots.
I find his expectations wildly counterintuitive, but then I've spent the last eight years or so beating my intuitive sense of how the world works into submission and rebuilding it on sounder lines. Otherwise, I'd never have passed the GRE...
As mentioned, for a projectile of a given mass, a higher muzzle velocity means more energy per unit momentum, and therefore more kinetic energy in the weapon per unit of recoil you feel. Ideally you want to fire extremely fast, very light projectiles; preferably a laser or a particle beam. If you can't manage megajoule-range particle beam shots, or are worried about dispersion at long range, a mass driver is your next best bet.
Also, higher shot velocity means longer effective range. The range at which you can hit a target in space with an unguided weapon is determined by how far they can dodge in the time it takes your shot to reach them; if they can move several times their own length before your bullet/laser/proton stream arrives, you miss. A lot.
The faster your shot moves, the greater the distance it can reach before the enemy has time to get out of the way. But that's a ship-to-ship issue, not a small arms issue.
I would muchly like to see an example of this.
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2010-01-22, 09:38 PM (ISO 8601)
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Re: Got a Real-World Weapon or Armor Question? Mk. VI
I think the argument was that the difference in recoil between a rail gun and a traditional gunpowder weapon would be marginal. This depends upon how much propellant is being used, relative to the mass of the projectile.
The recoil mounts in large guns wouldn't help much in zero-g. I'm trying to think of a good way to explain it. Basically a spring compresses because it has a force acting on one end, and something at the other end to prevent it from moving (e.g. the planet). So in space, you would need a lot of mass.
If you jetted the coolant you could probably use it to counter the recoil when the weapon is fired. Although this could be visible.
According to the wikipedia entries for both the railgun and coilgun they generate massive amounts of heat due to the electrical discharge. Superconductors could be used in vacuum, but currently they don't operate at room temperature.
Very safe weapons are something of an oxymoron. Concerning a personal weapon: I'm still wary about carrying around a charged up supercapacitor on my person. A few years off:
http://www.xkcd.com/678/
:-)
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2010-01-22, 09:48 PM (ISO 8601)
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Re: Got a Real-World Weapon or Armor Question? Mk. VI
Aristotle's Physics:
After three semesters of physics that's exactly the way that I felt. :-) Then I took a class on the history of science. In the second or third class the professor showed the results of an interesting experiment. If you ask people how a bullet travels (not directly, but in a clever way that reveals their intuition), even people who should really know better, will indicate that they expect the bullet to travel in straight line after it leaves the barrel! It was really enlightening, and gave me greater respect for Aristotle.
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2010-01-23, 06:51 AM (ISO 8601)
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Re: Got a Real-World Weapon or Armor Question? Mk. VI
And really, we all know that lighter objects fall slower than heavier ones, because of the "love" between the Earth and everything else. The bigger, and heavier, the object is, the more "lovable" it is, so it speeds more to meet the Earth. If you drop a big rock, it will fall faster than a small rock. Why bother with dropping rocks, it's just so obvious it's true, because it stands to reason.
Apparently, calling a physicist an Aristotelian is considered the gravest insult in some places.LGBTitP
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2010-01-24, 04:44 AM (ISO 8601)
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Re: Got a Real-World Weapon or Armor Question? Mk. VI
Hehe. I'm sure that's a good way to ingratiate yourself among physicists! ;-)
Actually, I think what your describing is Keplerian. If I recall correctly, the Ancient Greeks believed that "heavy" things fell because their natural place was at the center of the universe (and for similar reasons "light" things rose). I believe the word was "Telos"(?) which kind of means goal/purpose. Bigger things would have more Telos I suppose . . .
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2010-01-24, 07:04 AM (ISO 8601)
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Re: Got a Real-World Weapon or Armor Question? Mk. VI
The question of the monkey and the hunter:
A hunter aims his gun at a monkey in a tree. At the same instant the gun is fired, the monkey lets go of the branch he was hanging from.
How fast does the bullet need to go to hit the monkey, assuming no air resistance, friction, blah blah.
It doesn't matter (assuming the bullet reaches the monkey, and does not hit the ground first). If the bullet travels very fast, both it and the monkey have fallen very little, and the monkey is hit. If it goes much more slowly, both it and the monkey fall the same distance from the straight line trajectory, and the bullet still hits the monkey, even if the monkey was almost to the ground.
An example of how that sort of thing can be counterintuitive.
Edit:
Aristotle was a philosopher. Or if you want to be generous, a theorist. You do need experimentalists to see if the theorists are actually right.Last edited by huttj509; 2010-01-24 at 07:05 AM.
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2010-01-24, 07:38 AM (ISO 8601)
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Re: Got a Real-World Weapon or Armor Question? Mk. VI
Greeks had lots of systems, I was fairly sure that what I described was essentially Aristotelian (though it's been some time since I was looking at that stuff, so I might have got it somewhat mixed up). Certainly they recognized the universal attractive force, generally referred to as "love" (in some respects, superficially similar to gravity, but extended to all manner of phenomena). "Telos" is indeed the purpose, but it's more along the lines of "what is the purpose of the sun?" "It's to provide light and heat for living beings", etc. From modern scientific perspective, that was one of the main failures of ancient philosophy, the interest in "why?" rather than "how?" (the "how?" was still studied by craftsmen and engineers).
Last edited by MickJay; 2010-01-24 at 07:38 AM.
LGBTitP
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2010-01-24, 02:04 PM (ISO 8601)
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Re: Got a Real-World Weapon or Armor Question? Mk. VI
The recoil spring will do exactly what it does on Earth: spread out the force of the recoil so that you experience a smaller force over a longer time. In practice, this was introduced because it made for more stable gun mounts that were less likely to be damaged by the shock of firing.
In microgravity, the recoil springs (or hydraulics) will kill problems with accuracy. The real problem is the backwards drift you pick up from firing. But that's actually a very small force; one bullet does not have the momentum to send a ~100 kg object (like a man in a space suit) flying backwards, on either end of the gun.
Very safe weapons are something of an oxymoron. Concerning a personal weapon: I'm still wary about carrying around a charged up supercapacitor on my person. A few years off:
http://www.xkcd.com/678/
:-)
And rightly so; it means you either didn't get a physics education, or are both bloody-minded and too stupid to interpret the evidence in front of your eyes properly.
The real problem is that Aristotelean "physics" was not the same kind of animal as what we call "physics" today. Aristotle wasn't really trying to explain the physical mechanisms of motion and the nature of matter. He was trying to explain "why stuff moves" in the philosophical sense. Not "how do rocks fall," but "why do rocks fall?" And "rocks love to be closer to the ground" is as good an explanation for the philosophical-why of falling rocks as anything else.
This can be a surprise to physicists trying to read Aristotle's book Physics.
_______
Unfortunately, this was a problem with the ancient Greeks; they did not distinguish between subjects where "why" questions can be answered without regard to "how" questions and subjects where they can't. So they wound up with a whole array of notions about nature that make no sense at all. It's as if they'd asked "why are babies born?" and said it was all due to an elaborate stork conspiracy, because they thought the stork brings babies.
It's not just that the ancient Greek cosmology is wrong; it's that it's complete nonsense, based on unexamined assumptions and invoking whole categories of ideas and properties that have no basis in reality. To use a modern expression; it isn't even wrong; it's just gibberish.
This is why I reject the idea of people like Epictetus and Aristotle as early proto-physicists; I credit that to Archimedes, who actually bothered to do his homework before pronouncing that he'd unlocked secrets of the universe.
_______
Of course, this question bugs me, because it assumes the hunter is a lousy shot and neglected to allow for projectile drop. In the scenario as described, the monkey might have been just fine staying right where he was.
Someone needs to start a collection to buy that hunter a set of adjustable ladder sights.
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2010-01-24, 03:31 PM (ISO 8601)
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Re: Got a Real-World Weapon or Armor Question? Mk. VI
Because it is much easier to contain explosive force than raw electrical energy, when you can't just make a ground path (IE you aren't a fixed installation, planet-side. {deleted} Similar joules of explosives are much easier to use and safer to store, than that capacitor bank.
Of course, this question bugs me, because it assumes the hunter is a lousy shot and neglected to allow for projectile drop. In the scenario as described, the monkey might have been just fine staying right where he was.
Someone needs to start a collection to buy that hunter a set of adjustable ladder sights.Last edited by Norsesmithy; 2010-01-25 at 07:53 PM. Reason: Maybe I shouldn't post that sort of anecdote on the open forum
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2010-01-24, 03:37 PM (ISO 8601)
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Looking for data on the accuracy of firearms
I'm not sure if this is the right board but what the heck. I'm trying to write up a system to simulate more-or-less realistic modern firefights but my inability to find any solid data on anything but civilian firing ranges (all at very short distances, no less) blocks me at every turn. If anyone can link or direct me towards reliable sources I'll be very thankful.
Information on rifles and their ilk, accuracy at actually common engagement ranges, and military and/or commando grade firing range statistics is especially valuable.
P.S.: I'm not an US citizen and so cannot buy and download declassified Pentagon files (and I'm pretty sure I'm not allowed to have them, too)."All men dream, but not equally. Those who dream by night in the dusty recesses of their minds wake in the day to find that it was vanity; but the dreamers of the day are dangerous men, for they may act their dream with open eyes to make it possible." - T.E. Lawrence
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2010-01-24, 03:43 PM (ISO 8601)
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2010-01-24, 03:47 PM (ISO 8601)
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Re: Looking for data on the accuracy of firearms
I'm writing something from scratch, not modifying a system. d20 Modern has very little to do with reality but thanks anyway.
"All men dream, but not equally. Those who dream by night in the dusty recesses of their minds wake in the day to find that it was vanity; but the dreamers of the day are dangerous men, for they may act their dream with open eyes to make it possible." - T.E. Lawrence
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2010-01-24, 03:48 PM (ISO 8601)
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Re: Looking for data on the accuracy of firearms
I think that if you are willing to dive the depths it is located in, /k/ might be a better place to ask, just don't say I didn't warn ya.
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2010-01-24, 03:51 PM (ISO 8601)
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