Gun Generator: v0.1

[Jinumon]

Hello everyone!

So I've been working on the idea of a gun generator for quite some time. I've seen plenty of people recommend "The Cole Method," but I'm not much one for physics, and I was trying to come up with something that fits more into the game than into realism. Anyway, I wanted to run a Firefly game, but wanted a lot more variety to the TL9 conventional firearms. So, with that in mind, and using David Pulver's "Blaster and Laser Design" from Pyramid 3/37: Tech and Toys II as a basis, here's what I've come up with. But first, a few notes.

1) This is the very definition of a work in progress. If you see any blatant flaws, holes, or mathematical errors, I'd really appreciate you letting me know.

2) I'm hoping to update this as I get feedback and continue to work on it.

3) These rules will not allow you to recreate the standard weapons from GURPS: Ultratech, though it can get you pretty close. Those (and an ass-ton of algebra and playing with numbers) have given me the figures I've arrived with. These are simply as close as I could get.

4) There are some problems I simply could not solve on my own (like Range formulas), and so I made arbitrary decisions and have decided to post here in hopes that the community might be able to solve the problems I couldn't.

Gun and Launcher Design
Tech Level
For now all I have a decent workup is for TL 9. My experiences here and how well it's received will inform any work I do on later Tech Levels

Projectile
Again, right now all I have is for conventional guns. This is the very first workable version.
Conventional (TL9): A heavy, metal projectile, fired from a caseless cartridge. It inflicts piercing damage. Choose the type of piercing damage the weapon inflicts.

Barrel Array
This is the weapon's barrel and rifling system, which helps determine range. Decide if the weapon has a tiny (x0.1), very small (x0.25), small (x0.5), medium (x1), large (x2), very large (x4) or extremely large (x8) barrel-array relative to typical weapons of its class. Most weapons use a medium array, but a smaller array means reduced range with some saving in weight, while a larger array is heavier but longer-ranged.

Automation
Decide on the level of automation, which determines rate of fire.
Single Shot: The firearm can only fire one shot per second, but is lightweight.
Semi-Auto: The firearm can be built to fire at up to RoF 3.
Light Automatic: The firearm can be built to fire at RoF 4 to RoF 10.
Heavy Automatic: The firearm can be built to fire at RoF 11 to RoF 20.
Rotary: The firearm can be built to fire at up to RoF 40.

Damage Dice
Choose the dice of damage the weapon inflicts. The greater the damage, the heavier the weapon will be. Partial dice of damage can be specified as a decimal value. This will be converted to dice plus adds, but the decimal value is used for all other design calculation. Man-portable weapons should deal between 2d and 15d of damage, with pistols and carbines being nearer the bottom and anti-armor weapons being nearer the top.

Empty Weight
Calculate the weight in pounds based on the design decisions and this formula:

Empty Weight = (D x S / P)² x B x A
D is dice of damage.
S is 2 for most guns, or 1 for “super” versions of non-superscience guns.
P is 5 for conventional firearms.
B is for the barrel-array value: 0.25 for tiny, 0.5 for very small, 0.8 for small, 1 for medium, 1.25 for large, 1.6 for very large, or 2 for extremely large.
A is for automation value: 1 for single-shot, 1.25 for semi-auto or light automatic, 2 for heavy automatic, and 3 for rotary

Configuration
Holdout: The weapon is handheld, but may be shaped like a pistol or some other small device. This reduces Accuracy but lowers Bulk.
Pistol: The weapon uses a standard pistol grip.
Rifle: The weapon uses a carbine or rifle format with a shoulder stock and grip.

Weapon Statistics

Damage
Record the dice of damage chosen for the weapon. Conventional firearms have no armor divisor.

Accuracy
Accuracy depends on the weapon's configuration: 1 for Holdouts, 2 for Pistols, and 4 for Rifles.

Range
The weapon's half-damage and maximum ranges depend on the barrel array and dice of damage. Use the formulas below. Round range to two figures.
1/2D Range (yards) = D x D x Rb x Rt
D is dice of damage.
Rt is 22 pi-, 19 for pi, 16 for pi+, or 13 or pi++
Rb is based on the barrel-array: 0.1 for tiny, 0.25 for very small, 0.5 for small, 1 for medium, 2 for large, 4 for very large, or 8 for extremely large

Max Damage = 1/2D x Rb
Rb is based on the barrel array: x3 for tiny, x4.5 for very small, x6 for small, x9 for medium, x12 for large, x18 for very large, or x24 for extremely large.

Rate of Fire
Choose a RoF based on the weapon's level of automation and record it.
Single Shot: The firearm can only fire one shot per second, but is lightweight.
Semi-Auto: The firearm can be built to fire at up to RoF 3.
Light Automatic: The firearm can be built to fire at RoF 4 to RoF 10.
Heavy Automatic: The firearm can be built to fire at RoF 11 to RoF 20.
Rotary: The firearm can be built to fire at up to RoF 40.

Shots
Firearms are loaded with magazines, either classified as compact “Sticks” or bulkier, more efficient “Boxes.” Decide on how many rounds you want a chosen magazine to hold, and record the weight of the ammo. Then, calculate the weight of the empty magazine using the following formulas:
Stick Weight = (square root of Shots) x Wa x 6.7
Box Weight = (cube root of Shots) x Wa x 2.4
Wa is the weight per shot

Once the weight of the empty magazine has been calculated, add it to the weight of the ammo to determine the weight of a loaded magazine.

The size and type are typically up to the GM or the inventor of the weapon. However, keep in mind that guns with a magazine heavier than 1/2 of their empty weight are particularly unwieldy (additional -1 to Bulk, discussed later).

Reloading Time
The reloading time depends on the type of magazine: 5 seconds for Box magazine, 3 seconds for Stick magazines.

Weight
The weight of a firearm is its empty weight modified by the weight of a loaded magazine.
Weight = Empty Weight + Loaded Magazine Weight

Strength Requirement
Calculate the weapon's ST requirement using the formula below with loaded weight.
Pistol or Holdout ST = (square root of weight) x 6.3
Rifle ST = (fifth root of weight) x 6.3

Round to the nearest whole number.
If weapon is a rifle, append a dagger after ST to indicate two hands are used.

Bulk
Calculate Bulk using the formula below and express it as a negative number.
Bulk = (square root of weight) x SB
SB determined from the configuration: 1.5 for rifle, 1.25 for pistol, 1 for holdout.

Round Bulk to the nearest whole number and tack on a minus sign. However, the minimum Bulk is -3 for a rifle, -1 for a pistol, or 0 for a holdout; the maximum Bulk is -10

Recoil
Recoil depends on the size of ammunition fired from the firearm: 2 for pi- or pi, 3 for pi+, and 4 for pi++.

Cost
Cost depends on weight.
Cost = Empty Weight x Bc
Bc is $300 for conventional guns

Legality Class
Calculate the weapon's LC. The basic LC is 3 for conventional firearms. Reduce LC by 1 if the weapon exceeds RoF 3 or by 2 if the weapon exceeds RoF 20, and by 1 if it weight over 15 lbs. (loaded).

Skill Required
Any rifle configuration with a Bulk of -4 or greater, as well as Bulk -3 rifles with a RoF 3 or less uses the Guns (Rifle) skill.
Rifles that exceed RoF 3 and have a Bulk -3, as well as all Pistols that exceed RoF 3 use the Guns (SMG) skill.
Pistols with a RoF 3 or less use the Guns (Pistols) skill.

[PTTG]

I was thinking about something like this not long ago. Looks like you've done some good work!

[Dwarf99]

Whether you submit it for Pyramid or make your own PDF out of it, I'll be interested in seeing how this progresses.

[Jinumon]

Originally Posted by Dwarf99

Whether you submit it for Pyramid or make your own PDF out of it, I'll be interested in seeing how this progresses.

Wait, you can just submit things to Pyramid? Do they actually publish it? Do they take your idea, refine it, then publish it, or do they only accept finalized material?

Dammit, man! I need answers! ;)

[DouglasCole]

Originally Posted by Jinumon

Wait, you can just submit things to Pyramid? Do they actually publish it? Do they take your idea, refine it, then publish it, or do they only accept finalized material?

Dammit, man! I need answers! ;)

yes, nearly all (not all, but nearly all) Pyramid articles are submitted by the fan base. There are very specific style guides you must follow, and you'll want to look for the Wish List for an appropriate issue. A future "Tech and Toys" would be ideal.

But it MUST be finalized. You might want to check out the Pyramid Write Club, which helps starting authors.

[Dwarf99]

Originally Posted by Jinumon

Wait, you can just submit things to Pyramid? Do they actually publish it? Do they take your idea, refine it, then publish it, or do they only accept finalized material?

Dammit, man! I need answers! ;)

Yeah, you din't know?

[Jinumon]

Is there any chance I could get some math gurus to check some of mine? Like I said, some of the values (DAMN YOU, RANGE!) are arbitrary, and even I have to leave them as such, I'd prefer arbitrary values that are a little closer to accurate. If anyone is interested, I can send them (or post) a detailed breakdown of my work for examination.

[Varyon]

Originally Posted by Jinumon

Is there any chance I could get some math gurus to check some of mine? Like I said, some of the values (DAMN YOU, RANGE!) are arbitrary, and even I have to leave them as such, I'd prefer arbitrary values that are a little closer to accurate. If anyone is interested, I can send them (or post) a detailed breakdown of my work for examination.

Vehicles for 3e scaled 1/2D with the square root of damage (well, square root of bore size, but damage was linear with that) rather than with damage squared. Max scaled with the square root of 1/2D.

More realistically, 1/2D should be determined entirely by shape and weight of the projectile. For TL 4 weapons, I found that multiplying caliber (in inches) by 100 gives around the same 1/2D Range (in yards) as found in Low Tech. Max is more complicated, but 10x 1/2D is fairly consistent of GURPS weapons, so you could go with that.

If you're interested in designing firearms for GURPS, you may want to pick up 3e Vehicles (read through the entire weapon chapter before using it, however - there's a lot hidden in sidebars in odd locations, like appropriate bore sizes and barrel lengths for firearms in the section on mechanical artillery, and the important rules for handheld weapons not showing up until you're dealing with beam weapons). There are also some other things you'll need to come up with, like Rcl, MinST (although you could base that off how it works in 3e, then convert to 4e ST), Bulk, etc. Additionally, 3e had ~double the Acc values of 4e, so whatever Acc you calculate there should probably be halved.

[Dwarf99]

Originally Posted by Varyon

More realistically, 1/2D should be determined entirely by shape and weight of the projectile. For TL 4 weapons, I found that multiplying caliber (in inches) by 100 gives around the same 1/2D Range (in yards) as found in Low Tech. Max is more complicated, but 10x 1/2D is fairly consistent of GURPS weapons, so you could go with that.

I found out the 9mm in the basic set (1/2d 150) is more like 425xcaliber. I don't remember High Tech's 1/2d

[Varyon]

Originally Posted by Dwarf99

I found out the 9mm in the basic set (1/2d 150) is more like 425xcaliber. I don't remember High Tech's 1/2d

You'll really want to look at HT for a good idea of what might work there (I can't, as I don't have it). I will note that, looking at Tactical Shooting, Max being 1/2d x10 seems to work fairly well - shotguns (at least those firing shot, not sure about solid slugs) lean more toward 20x and LMG's more toward 5x, but otherwise it works decently well.

I should also mention that GURPS statistics typically don't follow the "1/2D is a multiple of caliber" rule, as for example an underpowered round actually has a shorter 1/2D. If you decide to go with this, just get it to match most weapons using full power loads and you'll be good. Note also that bullet shape also matters, so pistols will typically have a lower multiplier than rifles (as pistol bullets are shorter).