Steve Jackson Games - Site Navigation
Home General Info Follow Us Search Illuminator Store Forums What's New Other Games Ogre GURPS Munchkin Our Games: Home

Go Back   Steve Jackson Games Forums > Roleplaying > GURPS

Reply
 
Thread Tools Display Modes
Old 09-13-2016, 07:42 AM   #1
Icelander
 
Icelander's Avatar
 
Join Date: Mar 2006
Location: Iceland*
Default Swivel Guns (TL4-TL5)

I want to play around with shipboard ordnance that can be used for boarding and counter-boarding. Because smokepowder in my campaign is extremely expensive, there is an economic incentive to make efficient and accurate high quality guns, to avoid wastage of powder that costs at least $700+ per pound.

The presence of flying monsters and dragons with armoured skins also means that powerful and accurate guns capable of swiveling to engage flying threats are a much higher priority than during the historical Age of Sail.

What I want are basically three sizes. Let's call them 1) Mounted rifle, 2) 1-pounder and 3) 3-pounder.

One would be a more powerful musket, mounted on a pintle, tripod or some other flexible-but-stable mount, with a rifled barrel. It should be light enough to be used from a fighting top in the rigging, but powerful enough to outrange any personal weapon.

The 1-lb cannon should be light enough to be mounted pretty much anywhere on the deck or quarterdecks. It would be used with a round ball at range, grapeshot for boarding actions. If it could be used with canister, that would be great, but for such a small bore, I doubt it's worth it.

The 3-lb cannon should be powerful enough to shred boarders with canister as well as grapeshot. It would be capable of using round shot against flying threats or the rigging of enemy ships during maneuevering.

GURPS Low-Tech features the .69 caliber Lantaka (TL3) on LT p. 88 and the 2.25 caliber Swivel-Gun (TL4) on LT p. 89. The smaller Lantaka weighs 30 lbs. and has a pintle that weighs 13.5 lbs. The larger Swivel-Gun is 140 lbs. and comes with a 65 lbs. pintle.

There is also an interesting weapon on LT p. 93-93, the 1.06 caliber Wall Gun (TL4). Weighs only 27 lbs., comes with a 7 lbs. tripod.

In GURPS Fantasy, we find another Swivel Gun (TL4) on p. 144. This one is a 3-pounder, weighs 315 lbs., but doesn't specify whether that includes a pintle. It also has some statistical oddities, such as the Weight Per Shot being less than the nominal three pounds of the round ball, which contrasts oddly with the similar WPS of the smaller 2.25 caliber Swivel-Gun.

Some adjustments might have to be made to the stats of the Fantasy Swivel Gun. At the very least, it would be nice to know the assumptions behind the weapon, whether it's supposed to include the weight of a pintle, why the WPS is so low, etc. The Fantasy Maximum Range seems low for pretty much all the TL4 cannon there, too, comparing the stats to LT.

In any case, I'm going to want to come up with plausible and balanced stats for these three sizes of cannon. The designers will be TL4+1 with TL2+1 and TL3+1 assistants and TL4+1 materials are available, if necessary, i.e. if the benefits of extremely light and strong steel, springs, clockwork or other high-tech doodads justifies the cost. If high quality bronze works, then it's greatly preferred, because there are a lot of unemployed people in that field.

Because of many factors, the PCs have access to quite a lot of good quality bronze and bronzesmiths without any business, so figure bronze costs about half normal. Because of the vast variety of uses for good quality steel and the limited production of it, figure that +1 CF is added to steel items that are better than rehammered slag, i.e. Good quality steel costs double and the Fine versions cost even more.

I want to keep weight down as much as possible, though not at the cost of performance. Flexible, but stable mounts are a high priority, as these make the weapons much more effective. I'd also like to make these small cannon more powerful and more accurate.

Smokepowder, as noted earlier, is extremely expensive. This means that historical tactics that relied on using a lot of it, because it was cheap, are not viable. Any weapons that use smokepowder are potentially competing with heroic archers using enchanted arrows, not just regular archers and slingers. There exists some REF 0.4-0.5 smokepowder, but the variety that the PCs use is REF 0.8, comparable in power to early smokeless powder.

a) How can swivel-guns be made more accurate?

Whatever it is that allows the Wall Gun to have Acc 2 as compared to Swivel-Gun/Swivel Gun Acc 1, I'd want to replicate that in the larger calibers.

Would making a better pintle be enough? If so, how much more expensive than a regular pintle would that be? Would it weight more?

Would mounting the swivel-gun on a tripod work better than a pintle?

b) How much more power can the swivel-guns listed take without risk of bursting or other accident?

Using REF 0.8 smokepowder* instead of REF 0.4-0.5 black powder allows for either a smaller powder charge and the same power or more velocity from the same load. This does create more pressure, but a lot of historical cannon were significantly over-engineered, because poor quality control meant that the occasional barrel was flawed.

Assuming better quality control (to the tune of +2 CF or so), would the swivel-guns listed in Low-Tech or Fantasy be robust enough to fire those ca 1.5-lb and 3-lb iron balls at significantly greater velocities than listed?

c) If you load these smaller cannon with lead balls, instead of iron, how do the stats change?

*Which has gasses going at almost 4,000 fps, as contrasted with the less energetic black powder at around 2,000 fps.
__________________
Za uspiekh nashevo beznadiozhnovo diela!

Last edited by Icelander; 09-13-2016 at 08:02 AM.
Icelander is offline   Reply With Quote
Old 09-13-2016, 10:09 AM   #2
weby
 
weby's Avatar
 
Join Date: Oct 2008
Default Re: Swivel Guns (TL4-TL5)

First on the general idea of light artillery able to swivel and be accurate:

Wall gun vs swivel gun: I think it is mostly the TL 3->4 increase, metal working at TL 4 is more precise than at TL 3. Though things like possible barrel length and such might be a part of the reason.

I would allow the firearm quality modifiers for artillery too if someone uses the more accurate methods and has the skills and time to do such. Thus a TL4 base artillery piece with acc 2 could be made fine(accurate) with a lot of fiddling, specially if as you say you have access to TL 4+1 technology and likely magic measurements and such.

So I would basically start at the TL 4 cannon in LT, then use that extra care to increase the accuracy from 2 to 3 for fine(accurate).

A swivel mount is another thing:
It is a more complex construction than the basic artillery mounts presented.

Basically for something you can hold mostly in your hands the exact balance and such is not so important, if a 30lb weapon requires 1/3 of the weight in some part of the process to move it, normal people can well do such fairly easily. If a 300lb weapon is the same way, it is no longer a fast smooth process and you likely need several people. for a 1000lb weapon you can basically forget it.

That is why things like anti-air machine guns could have a simple pintle mount but something like a 20mm anti-air auto cannon needs a much heavier mount and a proper anti-aircraft artillery really big mounts.

I would likely go with:
The low weight weapons like a large musket could likely be mounted in a light and simple mount like a swivel or possibly a pintle.
A few hundred pound weapon would require something akin to an autocannon mount and might well be doable at TL 5, but would be heavier than the TL 6 versions.
Heavier weapons would not be fast to move at those TLs. Aiming requires a lot of muscle power and time, but making a mount that allows high elevations and such is not difficult if there is need, it it just the movement of such mass fast while at the same time supporting it when firing that is very hard.

As for more power:
The only example we have of comparable TL 4 and TL 5 cannons are the two 12lb cannons, the low tech "Cannon, 12-lb" and the High Tech "Bourges Mle 1853, 12-pounder".. The biggest difference seems to be the weight of the cannon being only about 1/3. But the damage seems to be 25% higher, despite that much lower weight.

On powder:
The TL 5 cannon seems to have half extra weight over the 12 lb base for the TL 4 cannon, so likely it then has higher REF powder.
__________________
--
GURPS spaceship unofficial errata and thoughts: https://gsuc.roto.nu/
weby is offline   Reply With Quote
Old 09-13-2016, 10:56 AM   #3
Icelander
 
Icelander's Avatar
 
Join Date: Mar 2006
Location: Iceland*
Default Re: Swivel Guns (TL4-TL5)

Quote:
Originally Posted by weby View Post
First on the general idea of light artillery able to swivel and be accurate:
It may help to think of my mounted rifle as an elephant gun* (somewhere around 2 to 4 bore) with a mount to make it easier to aim and maneuever and the 1-lb swivel cannon as a huge, short-barrelled 1-bore punt gun designed to fire ball as well as grape.

*Compare and contrast the Greener Elephant Rifle, 8-bore in HT p. 110. I want that, but with a heavier ball and higher velocity. To make it practical for a human to shoot, I accept that it will need a tripod or a pintle mount.

Quote:
Originally Posted by weby View Post
Wall gun vs swivel gun: I think it is mostly the TL 3->4 increase, metal working at TL 4 is more precise than at TL 3. Though things like possible barrel length and such might be a part of the reason.
The Swivel-Gun in LT and the Swivel Gun, 3-lb in Fantasy are both TL4, just like the Wall Gun. I think the lower Acc for the swivel guns is because historical swivel guns often lacked sights entirely and are stockless, whereas the Wall Gun is a stocked musket which happens to have a tripod mount to help with the weight.

So if I want Acc 2 swivel guns, I've got to mount them on something stabler than historical pintles and/or find a way to get a similar benefit to bracing them as a musket stock gives.

What is a good TL4 technological method of absorbing recoil that doesn't require a wheeled carriage or other bulky contraption?

The 65-lb pintle that comes with the 2.25 caliber Swivel-Gun in LT is presumably solid enough to absorb the recoil from that relatively low-powered cannon. On the other hand, if I wanted to launch a slightly smaller round ball, around 1-lb at full musket velocities from the Swivel-Gun, would such a pintle be solid enough?

Would placing a stock on the swivel-gun help any? Would it just break collar bones or would the pintle be enough to control the recoil well enough to prevent a human shooter from hurting?

Quote:
Originally Posted by weby View Post
I would allow the firearm quality modifiers for artillery too if someone uses the more accurate methods and has the skills and time to do such. Thus a TL4 base artillery piece with acc 2 could be made fine(accurate) with a lot of fiddling, specially if as you say you have access to TL 4+1 technology and likely magic measurements and such.

So I would basically start at the TL 4 cannon in LT, then use that extra care to increase the accuracy from 2 to 3 for fine(accurate).
Weapon Quality is available, yes, and the PCs have access to enough apprentices who can cast the Measurement spell so that they can be sure of exact measurements on several hundred things per day.

They probably don't use it on individual cannon balls, but they certainly have moulds, dies, calipers and gauges that have been hand-crafted by masters to magically-measured standards. And they'd probably use Measurement on any important and expensive single item, like a cannon or rifle barrel.

Quote:
Originally Posted by weby View Post
A swivel mount is another thing:
It is a more complex construction than the basic artillery mounts presented.

Basically for something you can hold mostly in your hands the exact balance and such is not so important, if a 30lb weapon requires 1/3 of the weight in some part of the process to move it, normal people can well do such fairly easily. If a 300lb weapon is the same way, it is no longer a fast smooth process and you likely need several people. for a 1000lb weapon you can basically forget it.
I'm curious what could be built at TL3-4, as well as what TL4+1 designs are possible.

There wasn't much need for anti-aircraft artillery before TL6 in our history, but with flying dragons, that's not true in fantasy worlds.

Historical TL2 mechanical artillery used tripods, including extremely heavy ones, and it would be natural for these to evolve into flexible anti-air mounts... assuming that metallurgy and engineering at TL3-4 allow for useful such mounts.

Quote:
Originally Posted by weby View Post
That is why things like anti-air machine guns could have a simple pintle mount but something like a 20mm anti-air auto cannon needs a much heavier mount and a proper anti-aircraft artillery really big mounts.

I would likely go with:
The low weight weapons like a large musket could likely be mounted in a light and simple mount like a swivel or possibly a pintle.
A few hundred pound weapon would require something akin to an autocannon mount and might well be doable at TL 5, but would be heavier than the TL 6 versions.
Heavier weapons would not be fast to move at those TLs. Aiming requires a lot of muscle power and time, but making a mount that allows high elevations and such is not difficult if there is need, it it just the movement of such mass fast while at the same time supporting it when firing that is very hard.
The Hotchkiss 1-pounder (HT p. 128) was TL5 and is both heavier and more rapid firing than any cannon I would consider practical for anti-air defence and boarding work for my PCs. Unfortunately, it doesn't say in the text how heavy the pintle for it is (though there is a nice picture).

Does anyone have an idea?

And does anyone know if such a pintle required high-quality spring steel or if it could be made from less costly alloys (or even bronze)?

Quote:
Originally Posted by weby View Post
As for more power:
The only example we have of comparable TL 4 and TL 5 cannons are the two 12lb cannons, the low tech "Cannon, 12-lb" and the High Tech "Bourges Mle 1853, 12-pounder".. The biggest difference seems to be the weight of the cannon being only about 1/3. But the damage seems to be 25% higher, despite that much lower weight.

On powder:
The TL 5 cannon seems to have half extra weight over the 12 lb base for the TL 4 cannon, so likely it then has higher REF powder.
The TL5 Napoleon 12-lb cannon uses 3 lbs. of Improved Black Powder (REF 0.5) to achieve a +25% boost in Damage and a +29% boost in Range* over what 6 lbs. of Corned Powder (REF) gets a TL4 12-lb cannon.

I'd guess that the TL4 cannon is assumed to be extremely inefficient and the balls substantially smaller than the bore, with a lot of the potential power being lost due to windage. As in our history, black powder was cheap and precision machining of ordnance was both expensive and politically and strategically difficult, this was an understandable design.

With smokepowder orders of magnitude more expensive than black powder in my campaign, there are much stronger incentives to hand-built cannon and shot carefully in order to maximise the yield from each precious ounce of powder.

So I'd want to get TL5 efficiency for my cannon, if possble.

*The Maximum Range of the Napoleon twelve pounder is only 2,000, but that's because of the elevation of the mount, the theoretical Maximum Range is 3,100.
__________________
Za uspiekh nashevo beznadiozhnovo diela!
Icelander is offline   Reply With Quote
Old 09-13-2016, 10:58 AM   #4
Polydamas
 
Join Date: Jan 2006
Location: Central Europe
Default Re: Swivel Guns (TL4-TL5)

I would ask Bill Stoddard directly if he remembers what he based his stats on, or just look up historical data and convert into GURPS stats. The Raymond J. Lord collection has an Elizabethan gunner's manual with barrel weights, calibers, and shot weights in PDF.

Not sure about the basis for the tripod of the Wall Gun. The basic idea of those weapons was that they had a hook, which you put over the parapet of your fort or gunnel of your punt or rail of your fighting top and transferred the recoil to it. But there were a lot of very light cannons/heavy muskets in South Asia, Iran, and South-East Asia and I don't know exactly how they were mounted.

Edit: Also, keep in mind that long narrow low-tech ships with masts roll a lot, and the higher above the waterline you go the worse the roll will be. They are not exactly platforms for precise gunnery, especially when firing directions other than fore and aft, and stabilization can only do so much if the platform that it is attached is rolling back and forth.
__________________
"It is easier to banish a habit of thought than a piece of knowledge." H. Beam Piper

This forum got less aggravating when I started using the ignore feature

Last edited by Polydamas; 09-13-2016 at 11:52 AM.
Polydamas is offline   Reply With Quote
Old 09-14-2016, 04:39 AM   #5
Icelander
 
Icelander's Avatar
 
Join Date: Mar 2006
Location: Iceland*
Default Re: Swivel Guns (TL4-TL5)

Quote:
Originally Posted by Polydamas View Post
I would ask Bill Stoddard directly if he remembers what he based his stats on, or just look up historical data and convert into GURPS stats. The Raymond J. Lord collection has an Elizabethan gunner's manual with barrel weights, calibers, and shot weights in PDF.
Well, I can recognise several potential models for the Low-Tech Swivel-Gun, although the weight is slightly more optimistic than most examples I can find.

I would welcome it if Bill Stoddard could chime in with Designer's Notes on the GURPS Fantasy artillery.

Is the Swivel Gun, 3-lb based on any particular archeological artifact or documentary evidence?

What were the underlying assumptions behind the weapon?

Does the Weight include or exclude a pintle and if a pintle is excluded, how much would one that could hold it safely weight?

Quote:
Originally Posted by Polydamas View Post
Not sure about the basis for the tripod of the Wall Gun. The basic idea of those weapons was that they had a hook, which you put over the parapet of your fort or gunnel of your punt or rail of your fighting top and transferred the recoil to it. But there were a lot of very light cannons/heavy muskets in South Asia, Iran, and South-East Asia and I don't know exactly how they were mounted.
A hook would do nicely for the lightest weapon I have in mind, a mounted rifle. Would the hook be lighter than 7.5 lbs.?

Quote:
Originally Posted by Polydamas View Post
Edit: Also, keep in mind that long narrow low-tech ships with masts roll a lot, and the higher above the waterline you go the worse the roll will be. They are not exactly platforms for precise gunnery, especially when firing directions other than fore and aft, and stabilization can only do so much if the platform that it is attached is rolling back and forth.
True, but Acc 1 gives effective range comparable to a pistol (or a thrown knife) and it is surely worth trying for effective range more in line with muskets (or throw spears).
__________________
Za uspiekh nashevo beznadiozhnovo diela!
Icelander is offline   Reply With Quote
Old 09-14-2016, 10:41 AM   #6
Polydamas
 
Join Date: Jan 2006
Location: Central Europe
Default Re: Swivel Guns (TL4-TL5)

Quote:
Originally Posted by Icelander View Post
A hook would do nicely for the lightest weapon I have in mind, a mounted rifle. Would the hook be lighter than 7.5 lbs.?
Probably. The biggest hook on a wall piece which I can remember from Graz was something like 4" tall, 1" deep at most, and probably narrower. I don't remember how much of that is iron and how much wood, but absorbing the recoil from something like a 1" caliber, slightly-more-than-musket-length barrel should not require anything huge.

"Wall pieces" were the oversized muskets for defending forts, "punt guns" were for fowling. Not sure if the ones for use on shipboard had a special name. The camel-borne ones from India and Iran had a special name.

Quote:
Originally Posted by Icelander View Post
True, but Acc 1 gives effective range comparable to a pistol (or a thrown knife) and it is surely worth trying for effective range more in line with muskets (or throw spears).
I can't speak for what in the Acc 0-2 range feels right for different designs. I would ask the forum member who used to be a pirate re-enactor, or the guys in Maryland with a replica of a 17th century brig. Sometimes they fire the swivel gun with a video camera nearby.

If you looked up the historical development of gunfounding techniques, you might get some ideas for what the workers in your setting can handle. Some of the books on the wrecks of the Spanish Armada talk about that, and there are dozens of coffeetable books with big print runs.
__________________
"It is easier to banish a habit of thought than a piece of knowledge." H. Beam Piper

This forum got less aggravating when I started using the ignore feature

Last edited by Polydamas; 09-14-2016 at 10:50 AM.
Polydamas is offline   Reply With Quote
Old 09-14-2016, 10:47 AM   #7
Ulzgoroth
 
Join Date: Jul 2008
Default Re: Swivel Guns (TL4-TL5)

Are you using the augmented Bracing bonuses from Tactical Shooting? Those will be of some help...
__________________
I don't know any 3e, so there is no chance that I am talking about 3e rules by accident.
Ulzgoroth is offline   Reply With Quote
Old 09-14-2016, 12:15 PM   #8
Icelander
 
Icelander's Avatar
 
Join Date: Mar 2006
Location: Iceland*
Default Re: Swivel Guns (TL4-TL5)

Quote:
Originally Posted by Ulzgoroth View Post
Are you using the augmented Bracing bonuses from Tactical Shooting? Those will be of some help...
I'm using those, yes.
__________________
Za uspiekh nashevo beznadiozhnovo diela!
Icelander is offline   Reply With Quote
Old 09-16-2016, 11:50 AM   #9
Icelander
 
Icelander's Avatar
 
Join Date: Mar 2006
Location: Iceland*
Default Re: Swivel Guns (TL4-TL5)

At TL4, breech-loaders like the Swivel-Gun can be reloaded much faster than muzzleloaders, but cannot withstand as much pressure and presumably lose some of the potential energy from the propellant through the breech.

At least, the low, low damage for the swivel guns in Fantasy and LT seems to suggest this.

Does anyone have an idea as to how much energy is lost through a breechloading design at TL4, compared to a muzzleloading one?

That is, with a gun of the same caliber, weight of shot and weight of powder, how much less Dmg and Range should one get?
__________________
Za uspiekh nashevo beznadiozhnovo diela!
Icelander is offline   Reply With Quote
Old 09-16-2016, 12:10 PM   #10
Whyte
 
Join Date: Oct 2008
Default Re: Swivel Guns (TL4-TL5)

Quote:
Originally Posted by Polydamas View Post
"Wall pieces" were the oversized muskets for defending forts, "punt guns" were for fowling. Not sure if the ones for use on shipboard had a special name. The camel-borne ones from India and Iran had a special name.
Zamburak:
https://en.wikipedia.org/wiki/Zamburak
Whyte is offline   Reply With Quote
Reply

Tags
artillery, cannon, fantasy, high-tech, low-tech

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Fnords are Off
[IMG] code is Off
HTML code is Off

Forum Jump


All times are GMT -6. The time now is 12:48 AM.


Powered by vBulletin® Version 3.8.9
Copyright ©2000 - 2024, vBulletin Solutions, Inc.