Different Gyroc Designs

[AlexanderHowl]

That is an absolutely terrifying projectile. The bullet (not including the casing or the powder) would weigh eight ounces and would travel 1000 yards/second. A homogenous object of that mass traveling that fast would slam for 120d of damage. It would possess a kinetic energy of over 90kJ (5x a .50 BMG) and I cannot even begin to imagine the recoil on that thing.

[Anthony]

Originally Posted by Varyon

I previously read gyrojets did spin, but then came across some mentions that spinning is bad for rockets, so assumed functional gyrocs wouldn't spin. If spinning does indeed work for rockets, that's a different story.

From what I remember, spinning causes issues with fluid flow for liquid propellant rockets, but that shouldn't be a serious issue for solid fuel rockets, and in any case it's not impossible to deal with, I've seen discussions of making rockets spin in ABM discussions (as a way of preventing ABM lasers from remaining focused on a particular point).

[Ulzgoroth]

A thought about gyroc merits: guided variants of conventional bullets are unlikely to be able to function in a vacuum. Stuffing in maneuvering thrusters rather than aerodynamic surfaces isn't very practical! But a guided gyroc could use thrust-vectoring and thus be able to maneuver in depressurized environments.

Originally Posted by Anthony

From what I remember, spinning causes issues with fluid flow for liquid propellant rockets, but that shouldn't be a serious issue for solid fuel rockets, and in any case it's not impossible to deal with, I've seen discussions of making rockets spin in ABM discussions (as a way of preventing ABM lasers from remaining focused on a particular point).

Spin stabilization has been used in both spacecraft stages (apparently, I just encountered that) and quite a lot in military rocket weapons. It's just fine for solid rockets.

[Joseph Paul]

Originally Posted by Fred Brackin

The fluff text in UT explicitly says that "Gyrcs" may not use spin stabilization though it suggests a Transhuman Space-ish michromechanical guidance system instead.

UT p144"Gyrostabillized rocket launchers fire spin-stabilized rockets the size of bullets."

Later in that paragraph is a line about not all "gyrocs" actually using spin - some use tiny aerodynamic surfaces.

[Rupert]

Originally Posted by Fred Brackin

That initial "stabilizer" is usually more like alunch rails than a barrel and in this case anthony's 17 calibers is going to be too long for a 15mm pistol. That's part of why I suggest just getting rid of the too inaccurate to be useful unguided gyrocs.

An alternative could be to use a low-pressure cartridge to fire the rocket/missile out of a lightweight barrel. That would give it enough velocity to be stable and reduce the risk of damage to the user. It would add some recoil energy, but in the case of automatic rifles and machineguns that can be useful for powering the feed system.

[Rupert]

Originally Posted by Varyon

The advantage of D is that distance to target isn't as important when you don't need to compensate for bullet drop, but ubiquitous rangefinders and HUDs could do away with that advantage as well.

At most small arms combat ranges (300m and under), when using rifles bullet drop isn't something you concern yourself with much. Trying to hit someone's head because it's only exposed part of them at 300m would be about the only time. The rest of the time, aim at centre of mass, fire.

The more gradual acceleration of a gyroc may allow for payloads that the sharp acceleration of a rifle makes unfeasible, but I don't know if there are any useful payloads that this would allow for.

One thing it should allow is larger payloads because the shell walls can be thinner. This is why bombs and mortar shells (sometimes also called 'bombs') have a bigger bang for their size than artillery shells (a 120mm mortar bomb has about the same effect as a 155mm artillery shell), and why tank guns tend to be a poor choice for firing HE shells (better than no fire support at all, of course).

[Rupert]

Originally Posted by Anthony

From what I remember, spinning causes issues with fluid flow for liquid propellant rockets, but that shouldn't be a serious issue for solid fuel rockets, and in any case it's not impossible to deal with, I've seen discussions of making rockets spin in ABM discussions (as a way of preventing ABM lasers from remaining focused on a particular point).

Spin is bad for HEAT warheads, and as those are by far the most common warhead on manportable missiles and rocket launchers, this is a very good reason to not spin them.

Artillery rockets generally do spin, though. Without spin they'd be even less accurate than they already are.

[Jack Sawyer]

Don't some finned projectiles still have some gyroscopic stabilization? I don't think its a binary in those cases.

I also forgot that there have been attempts to make fin stabilized EFP projectiles - another kind of 'fin formed' projectile I suppose. If you have forcefield technology there's no reason you couldn't 'forge' it without the explosion or a tapered bore.

[Rupert]

Originally Posted by Jack Sawyer

Don't some finned projectiles still have some gyroscopic stabilization? I don't think its a binary in those cases.

It's quite common for the spin to be imparted by the fins, by having them be angled. Another method is to have the rocket exhaust through several nozzles and cant them slightly.

Generally, unless the warhead dictates otherwise, you'll want an unguided rocket to spin, and a guided missile to not spin. There are exceptions, of course.

[Varyon]

Originally Posted by Rupert

At most small arms combat ranges (300m and under), when using rifles bullet drop isn't something you concern yourself with much. Trying to hit someone's head because it's only exposed part of them at 300m would be about the only time. The rest of the time, aim at centre of mass, fire.

A target 60 yards out will be reached in about 1/10th of a second by a typical (600 yards/second) rifle round. That becomes 1/5 s for 120 yards, 3/10 s for 180 yards, 2/5 s for 240 yards, and finally 1/2 s for 300 yards. At 60 yards, the bullet will drop about 2 inches, which isn't likely to make a difference unless you were aiming at the Vitals. At 120 yards, the bullet will drop over half a foot, enough to turn a headshot into a body shot or outright miss a shot to an outstretched arm. At 180 yards, the bullet will drop roughly half a yard, enough that a "center of mass" shot will probably hit the pelvis or possibly even a leg, and a shot to the lower leg (to avoid upper leg armor, perhaps) will hit the ground. At 240 yards, the bullet will drop just shy of a full yard, which will turn a torso shot into a leg shot, or a leg shot into a puff of dust on the ground in front of the target. At 300 yards, the bullet will drop by over a yard - a headshot will probably hit the abdomen, and a center of mass shot will hit the ground.

So, yeah, bullet drop is something that needs to be accounted for beyond fairly close range. Granted, a lot of combat tends to be in that short range, but when range is longer a flat trajectory will make it easier to hit what you're aiming at.

Originally Posted by Rupert

One thing it should allow is larger payloads because the shell walls can be thinner. This is why bombs and mortar shells (sometimes also called 'bombs') have a bigger bang for their size than artillery shells (a 120mm mortar bomb has about the same effect as a 155mm artillery shell), and why tank guns tend to be a poor choice for firing HE shells (better than no fire support at all, of course).

Sadly, gyrocs tend to be too small for HE/HEC to be of much use. Assuming that relationship (120mm mortar being equivalent to 155mm artillery) is fairly constant, 15mm HE gyroc would hold about as much explosive as 18.5mm HE, taking its 2d cr ex [1d-1] to 2d+2 cr ex [1d], which is an improvement, but probably not enough of one to make HE attractive in such a small caliber. HEAT (which I feel should be available at TL9 in 15mm, for 7d(5) imp) and APHEX are much better candidates for gyroc payloads.