Real Gauss pistol

[TJP]

Would the Real World (tm) gauss weapon (not a hobby gun) use fin-stabilized or spin-stabilized ammunition (or round pellets)? IIRC spin-stabilizing is not an option for "darts" with lenght-to-width ratio of 6:1 or more (as modern Discarding Sabot Depleted Uranium Fin-Stabilized "darts" with L/W ratios of 10:1, or so, demonstrate). The reason being (IIRC again!) that projectiles of such L/W ratios become unstable in flight if they're spun.

Do any of you have an idea how simple it would be to impart spin on a gauss projectile (not with rifling, but with magnetic fields)? If it is simple, I would guess (using only common sense, no scientific basis whatsoever) it'd be cheaper to make shorter darts (L/W less than 6:1) and spin-stabilize them rather than to build longer darts with fins and discarding sabots. It would be simpler (I guess) to build magazines for projectiles without fins (and sabots) and, as they'd be smaller, you could cram more of them in the magazine. So, making the spin-stabilized version more cost-effective.

Opinions?

 

[Zutroi]

Originally posted by TJP:
Would the Real World (tm) gauss weapon (not a hobby gun) use fin-stabilized or spin-stabilized ammunition (or round pellets)? IIRC spin-stabilizing is not an option for "darts" with lenght-to-width ratio of 6:1 or more (as modern Discarding Sabot Depleted Uranium Fin-Stabilized "darts" with L/W ratios of 10:1, or so, demonstrate). The reason being (IIRC again!) that projectiles of such L/W ratios become unstable in flight if they're spun.

Do any of you have an idea how simple it would be to impart spin on a gauss projectile (not with rifling, but with magnetic fields)? If it is simple, I would guess (using only common sense, no scientific basis whatsoever) it'd be cheaper to make shorter darts (L/W less than 6:1) and spin-stabilize them rather than to build longer darts with fins and discarding sabots. It would be simpler (I guess) to build magazines for projectiles without fins (and sabots) and, as they'd be smaller, you could cram more of them in the magazine. So, making the spin-stabilized version more cost-effective.

Opinions?

Taken as a given that gauss weapons are coilguns:

We make the gun a pair of coilguns, with the round between them, then we jacket the round with a magnet of it's own. Now as the round travels down the barrel, it tries to line up it's North with the next South down the barrel. By arranging our twin coilguns in the classic DNA double helix, we thus impart spin to the round.

 

[Aramond]

Unfortunately that won't work coilguns work on the solenoid principle, meaning the projectile has to travel the lines of magnetic force running through the hollow center of the coil.

Unless I have my magnetic wires crossed?

Aramond

 

[Zutroi]

Originally posted by Aramond:
Unfortunately that won't work coilguns work on the solenoid principle, meaning the projectile has to travel the lines of magnetic force running through the hollow center of the coil.

Unless I have my magnetic wires crossed?

Aramond

No, you'd be right for a typical non-magnetized projectile. If you magnetize the bullet the principle changes to being a pair of linear motors.

 

[mandelkubb]

Originally posted by TJP:
Would the Real World (tm) gauss weapon (not a hobby gun) use fin-stabilized or spin-stabilized ammunition (or round pellets)?

Fin-stabilization would need some kind of atmosphere to work, and the level of stabilization would be different depending on the thicknes of the atmosphere. Spin-stabilization would be preferrable but would, as said earlier, have other issues.

 

[Andrew Boulton]

Fin-stabilization would need some kind of atmosphere to work

Without an atmosphere, would it matter?

 

[mandelkubb]

Originally posted by Andrew Boulton:
Without an atmosphere, would it matter?

Now that you mention it - probably not.

Without atmosphere, only gravity will affect the projectile. Could the lengt of the projectile affect how it affected by gravity (in a way that matters?). The only problem I see is that the projectile could impact "sideways" which would affect penetration.

And the aim would of course have to be adjusted for atmospheric density and local gravity. But a high-speed projectile has a flat trajectory which should minimize the need for aiming correctins.

 

[vegascat]

The reason for a high lenght to width ratio is the penetration factor. Hyper speed impact tests showed that length was the prime factor in penetration, followed by projectile density and weight. On impact, the leading edge of the projectile vaporizes explosively, pushing in all directions, including on the projectile. A thinner longer projectile had less resistance from the vapor during impact, allowing deeper penetration. The limit of the penetration was when the trailing edge of the projectile vaporized, leading to the fact that longer projectiles had better penetration.
Spinning the projectile caused torquing forces on impact leading to the projectile not being in line with the primary penetration. The solution was a long fin stabilized dart.
As velocities increase, torque from spinning and vaporization problems increased.

 

[kaladorn]

Originally posted by vegascat:
The reason for a high lenght to width ratio is the penetration factor. Hyper speed impact tests showed that length was the prime factor in penetration, followed by projectile density and weight.

More correctly, putting a bunch of weight behind a small cross sectional impact area leads to penetration, no?

On impact, the leading edge of the projectile vaporizes explosively, pushing in all directions, including on the projectile. A thinner longer projectile had less resistance from the vapor during impact, allowing deeper penetration.

Up to the point where the projectile is thin enough it shatters, which is never desireable. There are minimum diameters based off of materials involved and forces in play. The better projectile is the longer, heavier projectile.... but heavy tends to oppose the velocity generation, and that is a key factor to downrange energy delivered. So, as in most things, there is a balance.

 

[Uncle Bob]

Kaladorn, I think Vegascat may mean exactly what he says. Hypersonic impacts are sometimes counter-intuitive. In some ways the actual length is more important than the sectional density.

 

[kaladorn]

Originally posted by Uncle Bob:
Kaladorn, I think Vegascat may mean exactly what he says. Hypersonic impacts are sometimes counter-intuitive. In some ways the actual length is more important than the sectional density.

Okay, I can believe that. At lower velocities, the amount of mass versus the surface area it exerts its effects over determine penetration.

But that wasn't the important point - the important point was that a certain minimum diameter of projectile (or perhaps I should say minimum overall structural strength which is often related to diameter) is required to prevent a penetrator from actually disintegrating (shattering).

 

[Anthony]

For impacts which exceed the speed of sound in the material used as an impactor, shattering is not relevant.

 

[Uncle Bob]

Originally posted by Anthony:
For impacts which exceed the speed of sound in the material used as an impactor, shattering is not relevant.

The speed of sound in steel is 4.5 Km/sec+. The speed in amorphous ceramics 5 km sec.
I don't think a gauss projectile moving at 1.5-2.5 km/sec is fast enough to ignore shattering.

 

[TJP]

For vehicular weapons I can see the need for high penetration, but not so with personal weapons (or should I say anti-personnel weapons)? Having a gauss pistol/rifle/MG that fires rounds at *very* high muzzle velocity and that have small cross-sections (or whatever the "nose area" of a round is called) would result in lesser wound damage as the round just punches through a soft target like a human body with relatively little damage (when compared to the penetration capability). Having a more moderate penetration would actually be better, when considering "stopping power" then. Or am I completely mistaken here? One could make gauss darts be "tumblers," like some assault rifle rounds are now, to enhance wounding capability, but how easy would that be with long rod penetrators?

 

[mandelkubb]

High velocity will give the projectile a flat trajectory, thus minimizing aiming errors due to misestimations of distance. It will also minimize the need to aim ahead of a moving target.

Keep in mind that modern weapons are designed to wound soldiers, not kill them, since a wounded soldier needs attention from other (medics, those who carry him to safety etc).

 

[kaladorn]

Originally posted by TJP:
For vehicular weapons I can see the need for high penetration, but not so with personal weapons (or should I say anti-personnel weapons)? Having a gauss pistol/rifle/MG that fires rounds at *very* high muzzle velocity and that have small cross-sections (or whatever the "nose area" of a round is called) would result in lesser wound damage as the round just punches through a soft target like a human body with relatively little damage (when compared to the penetration capability). Having a more moderate penetration would actually be better, when considering "stopping power" then. Or am I completely mistaken here? One could make gauss darts be "tumblers," like some assault rifle rounds are now, to enhance wounding capability, but how easy would that be with long rod penetrators?

If my target is wearing high tech body armour or a high tech vacc suit, a gauss pistol might not even be *enough* penetration for the task.

Ideally, a gauss pistol would have a controllable power output to allow you to 'dial it down' for unarmoured targets and 'heat it up' for the tin cans you have to shoot at. The flatter trajectory may encourage things like head shots to help offset the penetration versus tissue damage issue you bring up. I may only punch a small hole from your left eye out through the top of your spine, but it'll cause some problems....

The gauss pistol has evolved as a military arm designed to engage probably armoured targets (at least lightly armoured). There should be civilian variants, but there are also civilian weapons like LPL stunguns and puke lasers and the like that should fill in the self defense niche better even than projectile or conventional beam weapons.

 

[Uncle Bob]

A high velocity, long-rod finned penetrator has a very small crossection end on, but can cut a broad channel if it turns sideways.

Most pointed military bullets do yaw sideways, some more violently than others, as they encounter the stresses of passing though tissue. A gauss rifle penetrator could be designed to destabilize in a dense medium like flesh, perhaps even breaking into 2-3 subprojectiles for more damage.

[Gauss weapons and ACR APDS rounds must be spin stabilized. Fin stabilization doesn't work in vaccuum. And in case it comes up, you cannot spin a bullet enough to stabilize it in tissue.]

 

[Anthony]

Originally posted by Uncle Bob:
A high velocity, long-rod finned penetrator has a very small crossection end on, but can cut a broad channel if it turns sideways.

Finned penetrators, of course, are very stable in flesh (fins work just fine in flesh) and won't turn sideways, though they may break apart or deform.

 

[kaladorn]

Also, any ammo designed to tumble or fragment under certain conditions can find that design taken advantag of by armour designers. A layers composite armour could force the round to fragment or tumble *in the armour*.

 

[Uncle Bob]

The most unstable bullets (like the SEAL's new Mk263 bullets) take 1-5 cm to start tumbling. That is equivilent to 10-50 microseconds and to take advantage of the behavior armor would have to be unwearably thick.

Fragmenting bullets inevitably give up some penetration, but judging by the "shatter gap" experienced by brittle 76mm AP in WWII and the performance of the new FAPFDS ammo (Frangible Armor Piercing Finned Discarding Sabot, APFDS for AA guns) I would expect a 25-30% loss in penetration. That is equiviulent to a 10-15% loss in velocity, so I don't think it is significant in games terms.