[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.