GURPS Firearm Customization Draft 1

 GURPS Firearm Customization

A deeply modified AR-15 carbine. Base weapon is a variant of RRA LAR-15 (TS63), or one of dozens copies of the AR-15 present in GURPS. A maximum Ergonomics configuration with compensator.

    What is a firearm? A device to ignite powder, a metal tube to propel projectile and ideally a way to hold it all. Since it's inception, the core of the firearm has not changed. But as the centuries progressed, humans fell in love with firearms more and more. Dirty handgonnes gave way to beautifully fowling pieces fetching high prices from aristocrats. Brain-clubbing musket pistols were replaced with fine officer's handguns, a symbol of authority. The musket's offspring is a precision crafted sniper rifle, made of space age polymers, firing a scarce-material bullet around the horizon's bend. And as the proliferation and love of firearms grew, the desire to improve it, to make it yours grew exponentially, and thus the art of gunsmithing and firearm customization appeared.

    There are many reasons to improve firearms: make it more accurate, easier to handle, deadlier, more appealing. An average GURPS character will seldom have ability to create a fully unique firearm, that's why many resort to modifying their equipment to suit their needs. And since GURPS does not go into too many details on this matter, this work will try to improve the aspect of firearm modification within GURPS 4e.

Statement on worldview

    As with everything about GURPS, GURPS is a game for entertainment. I love GURPS realistic AND fun, and this work will reflect that. Where baseline 4e assumes something is 'below resolution' or 'a reason to take weapons bond', I will round it up to the point where it can finally be resolved and have tangible gameplay effect. Because of that, some parts of this article will be somewhat cinematic, but in a way that is expected of fiction that pays extreme respect to the firearm and the act of shooting it.

What firearms can be modified?

    Ostensibly, all of them. Firearms are made out of parts that were manufactured by a human being. An equally skilled human being could manufacture the same part - with improvements - and install it upon the base firearm. Indeed many firearms are simply variants of older design, improved in the blueprint and manufactured with modifications. Many locales have gunsmiths, professionals in the way of assembling and modifying firearms. A custom job is expensive, but sometimes worth it.

    Reasonably, a firearm that becomes a modification platform is mostly unheard of before TL6, with most firearms of that era offering what GURPS calls 'Accessories', an optic mount and maybe an engraving. More over, the firearm has to be popular, either widely adopted or experiencing massive commercial success. There's little reason to mass manufacture parts for a firearm that is not in use. Of course, custom parts shops are a rarity reserved for the rich until TL8, and manufacturing process before the advent of plastics is rather complicated. Don't expect a fully custom TL6 chassis for your M1921 Thompson Machine Gun.

    It is up to the GM and players to figure out what weapon has large enough parts aftermarket, but most TL7+ firearms do, especially mass-adopted platforms like Kalashnikov and AR-15/M16. Worth mentioning are TL6 wonders that are Colt M1911 and FN Browning HP, both still quite effective, used and with large aftermarket of parts.

How compatible is this system with baseline 4e solutions?

    Ideally, save for overlooked bugs, two systems are fully compatible and can be used together, separately or combining options. The important thing is to watch out for 'double dipping', gaining double benefit from effectively singular upgrade. As such, as part of this system, firearms will receive quality ratings such as Fine (Accurate), and the firearm will not be able to receive the same rating from another source, though it can become Fine (Very Accurate) if it receives the appropriate modification, for appropriate price. Do not allow firearms that are already half-way down the custom part tree to benefit from generalized upgrades. A firearm with free-floating barrel installed cannot be made Fine (Accurate) with a generalized option!

Part I: Modifying Firearm Parts

    Each firearm, or most of them, consists of six parts that directly affect it's performance in user's hands: 

Muzzle Device - A device attached to the barrel can alter firearm's behavior by way of directing and trapping gasses, or burning out the excess powder and gasses.

Barrel - the channel through which the bullet is propelled onward towards the target.

Chassis - Provisions for comfortably holding the firearm with both hands.

Controls - Elements of the firearm that engage it's functions - fire, safety, magazine ejection etc, as well as other internals.

Peripherals - Stock and/or grip for comfortably holding the firearm, shouldering it, directing it.

Only one of each, unless stated otherwise, can be present on a firearm. Many firearms already come with all or some versions of these parts. Whatever effect they have is included in the firearm's statistics table entry or firearm's description.

Each part can be optimized for either Ergonomics, Precision or Recoil Control. Each part, in addition to listed benefits, increases it's rating in these three fields. Consult the table below for effects of each rating. Ratings themselves are unneccessary for play, simply modify weapon's statistics and add appropriate notes to it's description. The ratings are non-cumulative, and each next step replaces the effects of the previous one.

Ergonomics Rating

Ergo 1	+1 to Holdout
Ergo 2	+1 to Holdout, +1 to fire in Close Combat
Ergo 3	+1 to Holdout, +1 to fire in Close Combat, Ignore -1 bulk from attachments
Ergo 4	Improve Bulk by 1

Precision Rating

Pres 1	Aiming for 4 seconds grants Acc+3 bonus.
Pres 2	Firearm is now Fine (Accurate), +1 Acc, if baseline firearm has 2 or more Acc.
Pres 3	Fine (Accurate), Aiming for 4 seconds grants Acc+3 bonus.
Pres 4	Firearm is now Very Fine (Accurate), +1 Acc, if baseline firearm has 4 or more Acc.

Recoil Control Rating

If you use fractional recoil rules, then each step simply reduces Rcl by 0.25 down to minimum of 1.

RclCtrl 1	Firing at ROF3+ grants +1 to Guns skill.
RclCtrl 2	Firing at ROF3+ grants +1 to Guns skill. Reduce Firearm ST by 1.
RclCtrl 3	Firing at ROF2+ grants +1 to Guns skill. Reduce Firearm ST by 1.
RclCtrl 4	Reduce Rcl by 1 to minimum of 1.

Part 1.1: Custom Firearm Parts

Firearm parts use Cost Factor (CF) as it appears on LT14. Tally up total CF, add +1 and multiply firearm's cost to find out it's final cost.

Each custom part, unless otherwise specified, grants extra -1 familiarity penalty.

Any combination of parts that amounts to +1 CF or more counts as Styling (HT11) for free, but only when dealing with those who appreciate modern or modified firearms. Too many gun owners prefer stock items!

Installing these parts is Adding Accessories (TS68) and is a complicated process.

Muzzle Device

• Flash Suppressor - An open, tube-like device that burns out excess gasses and powder, completely eliminating the muzzle flash. The shooter thus cannot be spotted by his weapon's flash and his view remains unobstructed. +1 Ergonomics, +0.25 CF, 0.1 lbs.
  Expensive version often serves as attachment base for a Quick-Detach Suppressor. +0.35 CF
  Cheap version is simply called Flash Hider (TS76), it does not improve Ergonomics.
  
• Compensator (TS76) - A small device covered in vents that redirects excess gasses that escape the barrel to counter-act weapon's recoil. +2 to Hearing and Vision rolls to locate shooter in the dark, Firearm ST-1, extra -2 familiarity penalty, +1 Recoil Control, +0.5 CF. Weight x1.1
  Expensive version often serves as attachment base for a QD Suppressor, which retains the Compensator's benefits while removing the bonus to locate shooter in the dark. +0.75 CF
  Cheap version is an attachment on many firearms and it's statistics already include it's effect. Firearm ST-1, +0.1 CF. No Recoil Control improvement.
  
• Unthreaded barrel - High quality Match barrels are often left without a thread in order to not disturb it's harmonics. Match barrel without a thread adds an extra +1 Precision, but the firearm loses it's ability to mount Muzzle Devices.

Barrel

• Pencil Barrel - Thin profile barrel decreases firearm's weight and changes it's balance. For purposes of sustained fire (HT85), it takes 75 shots to overheat. +1 Ergonomics, +0.25 CF, Weight x0.9
• Match Barrel - Named so for competitive matches, or for it "matching" the firearm perfectly. This barrel is either made to tight tolerances, or picked as best out of a manufacture batch. +1 Precision, +0.5 CF
• Bull Barrel - Also known as Heavy Barrel, weighting the barrel down reduces muzzle flip and allows longer sustained fire (HT85), treat it as Light Machinegun barrel. +1 Recoil Control, +0.5 CF, Weight x1.1

Chassis

• Free-Floating Chassis - Chassis that mounts in a way that does not come into contact with the barrel, increasing accuracy and stability by removing areas of excess clamping. Example is Hogue Free Float Tube. +1 Precision, +0.25 CF, x1.05 weight. Many handguns already come with free-floating chassis, it's stats are accounted for in firearm statistics.
• Low-Profile Chassis - Slim, lightweight chassis that sits as close to the barrel as possible, often opting for keyhole mounts instead of rails. Cutouts on exterior often expose the barrel. An example is Magpul MOE SL Handguard. +1 Ergonomics, +0.25 CF Weight x0.95.
• Heavy Chassis - Large chassis with ample space for accessories, sometimes with weighted inserts near firearm receiver. An example is M14 Modular Chassis by TROY. +1 Recoil Control, +0.5 CF, Weight x1.1

Controls

• Match Controls - Light trigger and precision fire control group ensure consistent pull that does not disturb the firearm. +1 Precision, +0.25 CF.
• Ergonomic Controls - Elongated switches and anatomical, streamlined shape greatly improve comfort of use. Grants Lightning Fingers (TS39) with this specific weapon. +1 Ergonomics, +0.25 CF.
• Recoil Buffer - Weights and rubber buffers are distributed in the receiver to lighten felt recoil. +1 Recoil Control, +0.5 CF, Weight x1.1

Peripherals

• Ergonomic Peripherals - Short stock like Troy M7A1 and a streamlined pistol grip allow for quick and comfortable work with the firearm. +1 Ergonomics, +0.25 CF, Weight x0.9
• Sniper Peripherals - Solid, often thumbhole stock with myriad of adjustments available: length of pull, cheek rest, extendable monopod. Allows for stable, user-specified shoulder position. +1 Precision, +0.25 CF, Weight x1.05
• Recoil Peripherals - Wide, often rubberized stock with solid, wide grip for best control and least recoil felt. +1 Recoil Control, +0.5 CF, Weight x1.1

Foregrip

• Angled Foregrip - This sort of foregrip allows for comfortable thumb-over-bore barrel handling and pressing the stock into the shoulder without turning it into a pivot point. +1 Recoil Control, $50, 0.5 lbs
• Handstop - This device prevents user's hand from slipping in front of the barrel or past the sweet spot for handling. User quickly achieves ideal grip by sliding the palm down the foregrip until it hits the handstop. +1 Fast Draw (Longarm or Pistol) when drawing into two-handed stance. +1 Ergonomics, $25, 0.1 lbs.
• Vertical Foregrip - See TS75. Multiply any fatigue lost from handling the weapon by 0.75

Part 1.2 Gunsmithing

See TS68. Just like before, watch out for double-dipping.

Custom barrel lengths

Many firearms can support different barrel lengths that alter it's performance. A spare barrel costs and weighs 20% of the firearm. Players may substitute the price of the barrel from an expensive firearm for a cheaper one if they share firearm family and caliber. Cheaper AR15 barrel for M16A4 will fit more expensive Mk 18 Mod 1 (HT121)

Installing a new barrel is a Adding Accessories (TS68) and is a complicated process.

Subcompact and Compact Barrels - See TS69.

Tactical Barrels - Barrels for use with suppressors. See Tactical Carbine.

Patrol and Long Barrels - This is an option that increases barrel length slightly. This is a difficult option to apply realistically because, while shortened barrel invariably harms performance, extended barrel does not ALWAYS improve it. At certain barrel lengths, the power of a projectile is wasted as it has to pass one tier of rifling after another. Most longer firearms and handguns can only benefit from Patrol barrel, while shorter carbines receive full benefit of a long barrel... And stop being carbines.

Patrol Barrel - Also called mid-length. Multiply Damage and Range by 1.1. +0.5 lbs. When used on an M4A1, it creates 16-18" Rifle akin to MK12 SPR.

Long Barrel - Multiply Damage and Range by 1.15, +0.75 lbs, +1 Acc, worsen bulk by -1. Super compact (like SMGs) or already lengthy firearms (like Sniper Rifles) will not be able to benefit from this.

Part II: Firearm Accessories

Tbd