[UT] Gun Generator v0.3

[Jinumon]

IT LIVES!!!!

Yes, guys, gals, and nonbinary pals, this is v0.3 to the GURPS Gun Generator I posted nearly TEN YEARS AGO. My how the time flies.

Anyway (for those of you who have been around long enough to remember), I am much happier with the extended nuance of this iteration. I have yet to settle on modifiers for smoothbore weapons and those that use preloaded barrels, but this does recreate ~90% of TL9 Conventional Guns with a degree of accuracy I’m pretty proud of. Of course, it’s all the guns it makes that aren’t in UltraTech that I’m excited about.

Immense thanks goes out to David Pulver (primarily for his work in Vehicles 3e and Pyramid 3/37: Tech and Toys II), The_Ryujin (for insights gleaned concerning ST from his GURB Ultra-Tech Quickie: More Blaster and Laser Design System Tweaks), and the astounding Christopher Rice (for inspiring me to dust this off after seeing the majesty that is GURPS Metatech).

Without further ado, happy shooting.

Jinumon

The Variables:
When designing an Ultratech firearm, there are only five primary variables to be determined. From these five variables, all weapon statistics can be derived. They are as follows.

Example: Joseph Knight of KnightArms Inc is looking to design a firearm that will take the Terran Confederacy by storm: the Cestus Heavy Pistol. We’ll follow him through the process to illustrate this system’s function.

Configuration, the type of firearm (pistol, rifle, or cannon)
Simply select a configuration. Types are ordered from smallest (and lightest) to largest (and heaviest).

Example: The Cestus Heavy Pistol, unsurprisingly, has a pistol configuration.

Bore Size, the diameter of the round, measured in millimeters
Select a round diameter. Larger rounds deal more damage, but will increase the size and weight of the weapon.

Example: Knight is looking for something large but still manageable. He likes the sound of “nine-one-one” and selects 9.11mm for the Bore Size.

Relative Power, an abstract measure of the propellant/projectile ratio (low, medium, high, or very high)
Select low, medium, high, or very high. Most pistols have a low Relative Power, while those classified as “magnum” rounds are generally medium. Most rifles have a high Relative Power, and very high is typically reserved for especially high-velocity rounds, such as those fired from an Anti-Material Rifle.

Example: This will be what truly sets the Cestus apart from other pistols. Instead of the usual “low” power, Knight selects the higher-velocity “medium,” and dubs the new round “9.11 Ravager.”

Barrel Multiplier, the length of the barrel, measured in multiples of Bore Size
Select a barrel length (in millimeters) and divide it by Bore Size to find the Barrel Multiplier. A larger Barrel Multiplier increases range, damage, and weight, albeit at a diminishing rate.

Example: Knight doesn’t want an unmanageably large weapon, though a little extra size is nice for intimidation. He selects a 140mm (~5.5in) barrel, for a Barrel Multiplier of 15.4.

Automation, the configuration of the firing mechanism (single-shot, semi-automatic, fully automatic, or rotary)
Select a level of Automation. Increasing Automation raises weight and rate of fire while reducing Legality Class. If you select “rotary” you must also select a number of barrels (typically 2 to 8).

Example: Any serious sidearm needs to have at least semi-automatic capabilities, and Knight wants to make sure the Cestus is available to civilian customers. He selects “semi-automatic” for its Automation.

Weapon Statistics:
Now that the variables have been selected, the individual statistics may be calculated

Damage (in dice) = Bore Size x Pd x cube root of (Barrel Multiplier) / 10
*Pd depends on Relative Power; 1.35 for low, 2 for medium, 2.3 for high, or 2.75 for very high

Round partial dice as follows:
Damage Under 1d: 0.01 – 0.32 = 1d-5; 0.33 – 0.42 = 1d-4; 0.43 – 0.56 = 1d-3; 0.57 – 0.75 = 1d-2; 0.76 – 0.95 = 1d-1; 0.96 – 0.99 = 1d
Damage Over 1d: 0.01 – 0.14 = no modifier; 0.15 – 0.42 = +1; 0.43 – 0.64 = +2; 0.65 – 0.85 = +1d-1; 0.86 – 0.99 = round up to next full die

Example: Joseph Knight’s new Cestus Heavy Pistol deals a whopping 9.11 x 2 x cube root of (15.4) / 10 = 4.53 dice of damage, or 4d+2.

Damage Type depends on Effective Bore Size, which is is determined by Bore Size and Relative Power

Effective Bore Size = Bore Size x Pt
*Pt depends on Relative Power; 1 for low, 1.1 for medium, 1.25 for high, or 1.5 for very high

Damage type is small piercing (pi-) for 7.99mm and smaller, piercing (pi) for 8.00mm to 9.99mm, large piercing (pi+) for 10mm to 14.99mm, or huge piercing (pi++) for 15mm and larger

Example: The Cestus Heavy Pistol has an Effective Bore Size of 9.11 x 1.1 = 10.02mm, just barely qualifying for large piercing (pi+).

Range is determined by Barrel Multiplier, Bore Size, and Relative Power

1/2 Damage Range = Barrel Multiplier^(2/3) x Bore Size x Ph x 5
*Ph depends on Relative Power; 0.65 for low, 1 for medium, 1.45 for high, and 2.05 for very high

Max Range = 1/2D Range x Pr
*Pr depends again on Relative Power; 11.5 for low, 8.5 for medium, 5.5 for high, and 4.5 for very high

After calculating both 1/2 Damage and Maximum Ranges, round each number to 2 significant figures.

Example: Joseph Knight’s new pistol has a 1/2D Range of 15.4^(2/3) x 9.11 x 0.65 x 5 = 282 yards. Its Max Range is 282 x 8.5 = 2,397 yards. After rounding, this gives the Cestus Heavy Pistol a Range of 280/2,400.

Accuracy is determined by 1/2D Range
Acc = square root of (1/2D Range) / 7, rounded to the nearest whole number

Example: The Cestus Heavy Pistol has an Accuracy equal to: square root of (280) / 7 = 2.39, which rounds to 2.

Rate of Fire is selected based on Automation.
1 for single-shot, 2 or 3 for semi-automatic, 4 to 15 for fully automatic, or up to 17 per barrel for rotary.

Example: As a semi-automatic weapon, the Cestus Heavy Pistol can have a RoF of 2 or 3. Joseph Knight selects 3.

Shots
Simply select the number of shots in a standard magazine. Keep in mind that the more rounds in a magazine, the heavier the loaded weapon will be.

Example: Eager to not overly burden the weapon, Joseph Knight selects an even 12 Shots for the standard magazine.

Weight = Empty Weight + (Weight Per Shot x Shots) + Magazine Weight

Empty Weight = Barrel Multiplier x Bore Size2 x Pw x Aw / 765
*Pw depends on Relative Power; 1.3 for low, 1.65 for medium, 1.75 for high, and 2 for very high
*Aw depends on Automation; 0.8 for single-shot, 1 for semi-automatic or fully automatic, or 1.4 (+0.6 per additional barrel) for rotary

Weight Per Shot = Bore Size3 x Pa / 20,000
*Pa is determined by Relative Power; 0.3 for low, 1 for medium, 1.6 for high, and 2 for very high
Round to 2 significant figures.

Magazine Weight = Weight Per Shot x Shots0.95 / 2
Round the weight of a loaded magazine (Weight Per Shot x Shots + Magazine Weight) to 1 significant figure.

Round Weight to 2 significant figures.

Example: The Cestus Heavy Pistol has an Empty weight of 9.112 x 15.4 x 1.65 x 1 / 765 = 2.76 lbs. Each round of 9.11mm Ravager weighs 9.113 x 1 / 20,000 = 0.038 lbs. Lastly, the empty magazine weighs 0.038 x 120.95 / 2 = 0.2 lbs. All told, the new pistol has a Weight of 2.76 + (0.038 x 12) + 0.2 = 3.42 lbs, with a loaded magazine weighing 0.656 lbs. Rounding results in a Weight statistic of 3.4/0.7.

An Alternate Method of Design
Because overall size and weight of a weapon is a major determining factor of whether or not someone will choose to use it, it may be advantageous to select the weight of the weapon ahead of time. To design a weapon this way, determine values for all of the five variables except Barrel Multiplier or Bore Size. With four of the five variables chosen, use the following formulas to find the last variable based on your selected Empty Weight.

Barrel Multiplier = Empty Weight x 765 / (Bore Size² x Pw x Aw)
or
Bore Size = [Empty Weight x 765 / (Barrel Length x Pw x Aw)]0.5

ST = (Weight / 10)^Cs x Css
*Cs depends on Configuration; 0.5 for pistols, 0.2 for rifles, and 0.35 for cannons
*Css also depends on Configuration; 18 for pistols, 9.5 for rifles, and 10 for cannons

Round to the nearest whole number. Listed values are one-handed for pistols, two-handed (†) for rifles, and mounted (M) for cannons.

Example: The Cestus Heavy Pistol has a required ST of (3.4 / 10)0.5 x 18 = 10.5, rounded to 11.

[Jinumon]

Continued...

Bulk, being a measure of both size and nimbleness, is calculated two ways, using whichever is worse.

The first method depends on Overall Length, which is determined by Barrel Multiplier, Bore Size, and Configuration.

Overall Length = Barrel Multiplier x Bore Size x Cl
*Cl depends on Configuration; 1.75 for pistol, 1.95 for rifle, or 1.55 for cannon

Bulk is -1 for 219.99mm and smaller, -2 for 220.00mm to 319.99mm, -3 for 320.00mm to 479.99mm, -4 for 480.00mm to 699.99mm, -5 for 700.00mm to 999.99mm, -6 for 1,000.00 to 1,499.99mm, -7 for 1,500.00mm to 2,199.99mm, -8 for 2,200.00mm to 3,199.99mm, -9 for 3,200.00mm to 4,799.99mm, or -10 for 4,800.00mm or larger

The second method is determined by Weight and Configuration.

Bulk = Weight^0.4 x Cb, rounded normally and made negative
*Cb depends on Configuration; 1.25 for pistols, or 1.5 for rifles and cannons

Maximum Bulk is -10.

Example: The Overall Length of the Cestus Heavy Pistol is 15.4 x 9.11 x 1.75 = 245.51mm, corresponding to a Bulk of -2. By weight, it has a Bulk of 3.4^0.4 x 1.25 = 2.04, or also -2 after being rounded and made negative. Its final Bulk is -2.

Recoil = Damage (dice) x Rt / Empty Weight^0.5, rounded normally
*Rt depends on Damage Type; 0.5 for small piercing (pi-), 1 for piercing (pi), 1.5 for large piercing (pi+), or 2 for huge piercing (pi++)

Minimum Rcl is 2.

Example: Joseph Knight’s new pistol has a hefty Rcl at 4.53 x 1.5 / 2.7^0.5 = 4.14, rounded to 4.

Cost = Empty Weight x $300
Round to 2 significant figures.

Example: The Cestus Heavy Pistol costs 2.7 x $300 = $810.

Cost Per Shot = Weight Per Shot x $20

Example: Each round of 9.11mm Ravager costs 0.038 x $20 = $0.76.

LC
Base LC for Conventional Firearms is 3. Reduce the LC by 1 if the weapon is fully automatic, or by 2 if the weapon is rotary. Reduce LC by an additional 1 (minimum 1) if Bore Size is 20mm or greater.

Example: The Cestus Heavy Pistol is LC3.

Sample Weapon: KnightArms Cestus Heavy Pistol, 9.11mm Ravager
Dmg 4d+2 pi+, Acc 2, Range 280/2,400, Wt 3.4/0.7, RoF 3, Shots 12(3), ST 11, Bulk -2, Rcl 4, Cost $810, LC3

[Phantasm]

Query: What modifications would be needed for:

- Electromagnetic/Gauss weapons?

- Revolvers?

- Very Low Power rounds (see: flare guns, shotguns, various grenade launchers)?



Overall, though, I like what you've done. I need to crunch numbers for a few cyberpunk pistols, though.

[Jinumon]

Originally Posted by Phantasm

Query: What modifications would be needed for:

- Electromagnetic/Gauss weapons?

- Revolvers?

- Very Low Power rounds (see: flare guns, shotguns, various grenade launchers)?

The_Ryujin already has an interesting work-up of EM weapons on his blog. IIRC, his findings indicated that EM weapons scaled their damage linearly with Barrel Multiplier, which makes sense as it's more room for accelerators.

Revolvers would take some fiddling but should be relatively simple (I hope). Same with Very Low Power, though I'll point out that Vehicles 3e seems to indicate that pistols and shotguns use the same Relative Power level (Low, in this instance). Not sure if the math bears out there yet or if that piece of info is considered out-of-date.

I'll play with the numbers and let you know.

Jinumon

[The_Ryujin]

Originally Posted by Jinumon

The_Ryujin already has an interesting work-up of EM weapons on his blog. IIRC, his findings indicated that EM weapons scaled their damage linearly with Barrel Multiplier, which makes sense as it's more room for accelerators.

Revolvers would take some fiddling but should be relatively simple (I hope). Same with Very Low Power, though I'll point out that Vehicles 3e seems to indicate that pistols and shotguns use the same Relative Power level (Low, in this instance). Not sure if the math bears out there yet or if that piece of info is considered out-of-date.

I'll play with the numbers and let you know.

Jinumon

The muzzle energy of an EM gun can be roughly broken down into the length of the rails/coils times the volume of the rails/coils times how powerful they are. So it should realistically be the square root of the increase of the barrel.

Railguns are going to be simpler and lighter (and cheaper) for a given output but have crap barrel life (making them better for guns that are going to have low barrel lives even with normal guns like Tank guns and artillery). They're also going to be much loader and have a significant muzzle flash.

For revolvers, if its a convectional gun remember that the chamber is basically the chamber so it's basically a magazine that has to be strong enough to handle the firing force of the weapon. A good place to start is to look up the weight of the cylinder of different revolvers and divide their weight by bullet they fires WPS, number of rounds it holds and the muzzle energy of the weapon and see if any trends emerge. If the weapons is a EM revolver then the cylinder is just a stylistic magazine.

[CaptainBetts]

I absolutely love this system, and it's created a lot of "feels right" results for me through a lot of use over the last few weeks.

I was wondering whether you saw this from David Pulver - is this taken into account in the system? Figured I'd flag it just in case, I guess the L/D ratio is the equivalent of the "Relative Power" stat?

Originally Posted by David L Pulver

(On Accuracy: You lose one point from Acc if the projectile L/D ratio is under 4:1 or the caliber is below 7mm.)

I'll be following your Gun generator threads with high levels of support.

I'm curious if you've tried working out things like Shotguns/Gyrocs etc. (though Gyrocs are admittedly an entirely different class of weapon).

Originally Posted by Jinumon

Same with Very Low Power, though I'll point out that Vehicles 3e seems to indicate that pistols and shotguns use the same Relative Power level (Low, in this instance). Not sure if the math bears out there yet or if that piece of info is considered out-of-date.

For clarity, would you suggest using "firearm" configuration with Low power to represent shotguns? Not sure exactly how to work out things like the Shots characteristic and how that impacts things.

As I recall, there was some comment (can't remember if it came from Pulver himself) that the anti-materiel rifle should have been LC2 - I've tended to reduce the LC of weapons with "very high power" with this system by an additional -1.

[Alden Loveshade]

I thought people who are interested in this thread might be interested in this playtesting!

Call for Playtesters: GURPS Guns

[Varyon]

Originally Posted by Alden Loveshade

I thought people who are interested in this thread might be interested in this playtesting!

Call for Playtesters: GURPS Guns

Oh, that should be good. I'm strongly tempted to apply, although I wouldn't want to risk bumping off someone who had a more-suited skillset to the task. I'll certainly need to give it a good think.

...

I need to give this system a proper readthrough before I have anything really worth saying. One thing I will note is that I'm leery of how the Barrel Multiplier factors into the damage. With the gun design system from VDS, damage roughly scaled linearly with absolute barrel length (it was essentially BorexLength, but Length was in multiples of Bore and was only available in a few distinct sizes rather than being able to be arbitrarily set, which concealed the linear relationship). Of course, that assumed the propellant was always scaled to be optimal for that weapon's barrel length, while it sounds like yours may be essentially using the same ammunition for any, say, 9.11 Medium Power firearm, regardless of barrel length.

[The_Ryujin]

Originally Posted by CaptainBetts

I absolutely love this system, and it's created a lot of "feels right" results for me through a lot of use over the last few weeks.

I was wondering whether you saw this from David Pulver - is this taken into account in the system? Figured I'd flag it just in case, I guess the L/D ratio is the equivalent of the "Relative Power" stat?

L/D ratio is the length to diameter to diameter ration; that is how long the round is relative to how wide it is. This plays a part in figuring kind of Piecing modifier the round will have (a long round will create a bigger wound cavity as it tumbles), how heavy it will be, and affects it's range.

[RogerBW]

Originally Posted by Varyon

Oh, that should be good. I'm strongly tempted to apply, although I wouldn't want to risk bumping off someone who had a more-suited skillset to the task. I'll certainly need to give it a good think.

Your call of course, but the more people apply, the more we get to choose the people we think will be most helpful on the project.

Just in case, I should probably say again that this playtest isn't for any kind of "GURPS Gun Design". You don't start from scratch and design a pistol as you can with the system in this thread. You start with real-world numbers and get out GURPS stats that should be reasonably consistent with the stats already in High-Tech etc..