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Found this interesting tid-bit about the first Gyrojet pistol on a gun site. This essentially means that the "bolter" was invented in the '60s.

http://www.genitron.com/unique13.html

Technically bolters fire the round conventionally then the rocket fires at a pre specified distance. This prevents the issues the Gyrojet ran into. Very specifically poor accuracy and worthlessness in close combat (the only kind of combat pistols see).

The AA-12 MPS (particularly when loaded with the grenade option) has always struck me as the most bolter like of modern fire arms:

http://www.youtube.com/watch?v=bhDPoVm74To&feature=related

Bolt type weapons are still less effective than conventional shells for the following reasons.

Acceleration in the barrel is low, reducing its effectiveness in imparting accuracy to the round.

Rocket propelled rounds can't be spun as it disperses the exhaust and reduces its propulsive effect.

Any wobble of the bullet as it exits the muzzle is amplified by the rocket thrust.

Inaccuracies in the manufacturing of the rocket motor, the fuel and the exhaust nozzles, cause more wobble during flight.

The effective density of the round is less than a solid shell, and varies during flight as the fuel is burnt. This means that velocity dropoff is faster than with a conventional round.

While these factors would be ameliorated by high-tech production techniques, it is still better to avoid them altogether. Advanced engineering would better be applied to producing more effective conventional rounds. KISS is a good engineering principle.

The rocket propelled round predates the 1960's Gyrojet. During WW2, the Japanese had a 40mm aircraft mounted gun which fired a kind of semi-rocket shell. The shell contained the propellant and burnt it in the breech and barrel.

http://pwencycl.kgbudge.com/J/a/Japanese_40mm_Ho-301_gun.htm

All in all, the Bolt gun is a silly weapon, but this is an SF game so what the heck?

Kilkrazy wrote:Rocket propelled rounds can't be spun as it disperses the exhaust and reduces its propulsive effect.

That would appear to make sense, but why is the rocket laucher on the german Sturmtiger rifled?

The Sturmtiger was a highly specialist vehicle for shooting large demolition charges.

The 380mm rocket mortar was a semi-experimental design. It had to compromise between firing a large shell, a light and small enough enough gun to fit into the vehicle, and firing the gun without blowing itself and the vehicle apart.

The rocket assistance allowed this to be done by reducing the breech pressure, and getting more range with rocket assistance. This came at the expense of range and accuracy. It was a sensible compromise given that buildings are large, static targets and easy to hit.

Naval rifles of similar calibre have much better range, armour penetration and accuracy, but they are much larger and need to be carried on vehicles the size of railway carriages.

Howard A Treesong wrote:

Kilkrazy wrote:Rocket propelled rounds can't be spun as it disperses the exhaust and reduces its propulsive effect.

That would appear to make sense, but why is the rocket laucher on the german Sturmtiger rifled?

They don't even NEED rifling to achieve spinning, they can use a part of their rocket exhaust to create spin motion.
Just picture one of those fireworks that start to spin after you ignite them.
In the end it's the same tradeoff as rifling, you sacrifice power to gain accuracy.

ShumaGorath wrote:Technically bolters fire the round conventionally then the rocket fires at a pre specified distance. This prevents the issues the Gyrojet ran into. Very specifically poor accuracy and worthlessness in close combat (the only kind of combat pistols see).

According to which fluff?!!?!?! I want references!

I just think this is neat because I always thought that a gyrojet was just a sci-fi weapon, I had no idea anybody had ever tried to do one in real life, left alone 50 years ago!

nostromo wrote:

Howard A Treesong wrote:

Kilkrazy wrote:Rocket propelled rounds can't be spun as it disperses the exhaust and reduces its propulsive effect.

That would appear to make sense, but why is the rocket laucher on the german Sturmtiger rifled?

They don't even NEED rifling to achieve spinning, they can use a part of their rocket exhaust to create spin motion.
Just picture one of those fireworks that start to spin after you ignite them.
In the end it's the same tradeoff as rifling, you sacrifice power to gain accuracy.

It's true you can spin a rocket projectile by firing sideways pointing motors. However, this increases the problem of unbalanced rocket firing cause course deviations.

In cases where the rocket wants to be spun for accuracy, it is easier to do it by rifling the launch tube.

BigToof wrote:

ShumaGorath wrote:Technically bolters fire the round conventionally then the rocket fires at a pre specified distance. This prevents the issues the Gyrojet ran into. Very specifically poor accuracy and worthlessness in close combat (the only kind of combat pistols see).

According to which fluff?!!?!?! I want references!

The dark heresy books make mention of it a few times. And its stated in multiple places elsewhere. Its why they eject spent shell casings.

Kilkrazy wrote:
It's true you can spin a rocket projectile by firing sideways pointing motors. However, this increases the problem of unbalanced rocket firing cause course deviations.

No it's the exact opposite:

Picture an unbalanced rocket that isn't spinning, part of it's exhaust is pointing sideways, the deviation accumulates in this direction and the rocket will fly circles.
Picture an unbalanced rocket that is spinning round it's axle, part of it's exhaust is still aimed sideways in unbalanced fashion, BUT the spinning makes that this deviation is sequentially applied to all directions, thereby nullifying it over the course of one rotation. The result it stays on it's initial trajectory albeit it move forward in a corkscrew fashion.

BigToof wrote:

ShumaGorath wrote:Technically bolters fire the round conventionally then the rocket fires at a pre specified distance. This prevents the issues the Gyrojet ran into. Very specifically poor accuracy and worthlessness in close combat (the only kind of combat pistols see).

According to which fluff?!!?!?! I want references!

The novels from the Draco-trilogy describes the sound of a bolter as 'raaark-pop-swooosh-thud-crump'
The explanation went something like:
'raaark' - the initial charge goes off to eject the bolt from the gun
'pop' - bolt exits barrel
'swoosh' - propellant ignites accelerating the bolt
'thud' - bolt makes contact with fleshy body
'crump' - bolt explodes internally

Isn't angling the casing and leading edges wiser than the exhaust? Throw a fin onto the rocket and you get the same effect without loss of thrust.

That sort of spin is not providing centrifugal course stabilisation. You get that from axial spin.

Also, a rocket flying a corkscrew path will have a shorter range than a rocket flying a straight path.

Consequently, it is better to stabilise rockets with fins and by spinning them by rifling the launch tube.

Also, you still have the problem of thrust variation. Suppose the corkscrewing rocket spins 10 times a second. And suppose there are defects in the motor casting that cause a slightly weaker burn every 10th of a second. This would tend to drive the rocket off course.

BigToof wrote:Found this interesting tid-bit about the first Gyrojet pistol on a gun site. This essentially means that the "bolter" was invented in the '60s.

http://www.genitron.com/unique13.html

You only live twice. Or so it seems...

ShumaGorath wrote:

BigToof wrote:

ShumaGorath wrote:Technically bolters fire the round conventionally then the rocket fires at a pre specified distance. This prevents the issues the Gyrojet ran into. Very specifically poor accuracy and worthlessness in close combat (the only kind of combat pistols see).

According to which fluff?!!?!?! I want references!

The dark heresy books make mention of it a few times. And its stated in multiple places elsewhere. Its why they eject spent shell casings.

Not good enough. You gotta use the main rule books, none of this "I just got hired to write some gun porn for the 40K universe. I *could* do some research, or I could just smoke up, and write whatever comes to mind," Black Library crap. That's apocryphal, and not officially recognized cannon!

Actually a lot of it is, and the dark heresy books are recognized canon. Just because its not in the rulebook doesn't mean it didn't happen in the main universe.

Also rockets don't have shell casings and a rocket launching in an enclosure with no backblast is already little different than a bullet from the perspective of the weapon.

ShumaGorath wrote:Actually a lot of it is, and the dark heresy books are recognized canon. Just because its not in the rulebook doesn't mean it didn't happen in the main universe.

Not in my book! I'm forming my old splinter cult. 40K according to BigToof!

ShumaGorath wrote:Also rockets don't have shell casings and a rocket launching in an enclosure with no backblast is already little different than a bullet from the perspective of the weapon.

Or, maybe they're just attempting to explain an element that was added by the artists to add excitement and drama to their work, without necessarily having an original rational in the sittuation....

Welcome to 40k you must be new here. Thats how all of it works. Or do you think chainswords make sense?

ShumaGorath wrote:Welcome to 40k you must be new here. Thats how all of it works. Or do you think chainswords make sense?

Nah, I've been playing since RT, that's how I know that the fluff changes everytime Rick sneezes....

Oh, and the chainsword thing was stolen from another GW game, Chainsaw Warrior, which I've also played.

Kilkrazy wrote:That sort of spin is not providing centrifugal course stabilisation. You get that from axial spin.

As my previous post stated the corkscrew motion of an unbalanced rocket happens BECAUSE they're axially spinning to begin with, if they weren't spinning they'd go off course in a wide circle.

Kilkrazy wrote:
Also, a rocket flying a corkscrew path will have a shorter range than a rocket flying a straight path.
Also, you still have the problem of thrust variation. Suppose the corkscrewing rocket spins 10 times a second. And suppose there are defects in the motor casting that cause a slightly weaker burn every 10th of a second. This would tend to drive the rocket off course.

A rocket with constant & symmetric exhaust is better than one with inconsistent/asymetric exhaust, that's true for all rockets, isn't it?

Kilkrazy wrote:
Consequently, it is better to stabilise rockets with fins and by spinning them by rifling the launch tube.

Both of these options also reduce the power/range of the rocket. But ultimately neither you or i have the actual numbers to decide which reduction of power gains the most accuracy. I can only assume this type of rocket went out of fashion for a good reason so i won't be arguing which is better. I just wanted to show that the principles applied in such rockets work and have been used in combat.

nostromo wrote:

Kilkrazy wrote:
Consequently, it is better to stabilise rockets with fins and by spinning them by rifling the launch tube.

Both of these options also reduce the power/range of the rocket. But ultimately neither you or i have the actual numbers to decide which reduction of power gains the most accuracy. I can only assume this type of rocket went out of fashion for a good reason so i won't be arguing which is better. I just wanted to show that the principles applied in such rockets work and have been used in combat.

FWIW, it seems that that was the next approach. Basically a set of fins in the shell that extended during firing.

I believe that it went out of fashion because they were unable to get the accuracy up with the angle nozzles approach. I wonder what it would be like with more modern manufacturing....

Interesting article here concerning rockets

http://www.pt-boat.com/rocket/rocket.html

Accuracy
4.5-inch ground launched fin stabilised rocket = 20-40 mil
5-inch ground launched rocket with spin stabilisation = 20 mil
Aircraft launched fin stabilised rocket = 6-8 mil
Gun (general) = 1 mil

I don't know what a 'mil' is, though obviously a small mil is good.

Accuracy of the missiles has to be gauged against the cost of manufacturing them. Perhaps basic fins are cheaper to make than sophisticated spinning nozzles

Modern manufacturing would undoubtedly improve the accuracy of casting or machining the rocket nozzles and moulding the propellant. So this would help improve accuracy.

OTOH improved manufacturing would tend to improve many aspects of weapons -- rockets would not be the only beneficiaries.

BTW it seems I misunderstood your description of rockets corkscrewing. I thought you meant they would follow a spiral path, in other words orbiting their axis of forward motion. I doubt this would be very accurate method. However it seems that the spun rockets spin much like the shell from a rifled gun.