These rules are heavily inspired by the work started by Ken Hood, which can be found here. However, those rules are not nearly comprehensive enough to cover the full possibilities of firearms, and most d20 rules fall far short of what would be ideal. With that in mind, I'm going to be borrowing heavily from Borderlands, as well as using a facsimile of Pathfinder's "race builder" rules, to build a set of rules for customizable guns.

Overview

Firearms in Trinity have been relatively ever-present, being an expression of Technology once it begins showing up. It's entirely possible to find ancient guns built by the Arkeyans, the Ronkans, or other civilizations that have been lost to time. In modern Trinity, guns have become a common part of life, and their use is near-ubiquitous among those that aren't specialized in melee combat or Forces that oppose Technology.

Guns are dangerous, and it's relatively easy to become proficient in their use. However, guns are also ranged weapons, which means that they can hurt your allies in a tight situation. While most people realize that guns are superior in most ways, they have several drawbacks that make most cautious to use them. There's a reason swords are still more common: it's almost impossible to accidentally cut your allies, and even if you do, you won't turn them into paste the way most guns of any strength will.

Complexity, Type, and Subtype

Every gun falls into one option from three main categories: complexity, type, and subtype. These are explained here.

Complexity

Complexity has three ratings.

Basic
Advanced
Complex

A basic firearm is incredibly easy to learn to use, and has few moving parts or complicated pieces. Every component on a basic firearm has an obvious function, even to those unfamiliar with guns.

Advanced firearms are harder to use, usually due to having multiple firing options, more complex loading mechanisms, or unexpected functions that aren't obvious at first glance. Advanced firearms will sometimes have accessories attached that don't have a clear function unless you know what you're looking at.

Complex firearms are the most difficult to use, requiring familiarity with their function. While these weapons still retain the "point and click" interface that makes guns popular, their more advanced settings and more complicated Technological functions mean that just pointing the gun at someone and pulling the trigger may make all sorts of interesting things happen, depending on the weapon's settings. The full functionality of a complex firearm is difficult to ascertain from cursory inspection, even for someone proficient in other complex firearms.

Complexity and Proficiency: Firearms begin simple and basically identical across types, then explode into diversification as technologies become more sophisticated. For this reason, firearm proficiency feats are a bit unusual, and the more complex the firearm, the more specialized the proficiency becomes. See the Feats section at the end of this page for more information.

Type

Firearms have six general types.

Pistol: Versatile class of weapons usually suited to short-to-medium range combat, typically with fast reload speed. Sub-types include auto-firing machine pistols with larger magazines but lower accuracy, middle-of-the-road repeaters, and revolvers with longer range and higher accuracy but slower reloads and lower ammo capacity.
SMG: High rate of fire and low recoil, good at close range and decent at medium range. Usually lower per-round damage than pistols of lower level, but greater rate of fire means higher DPR, and tend to have high capacity magazines.
Shotgun: Fire multiple pellets, effective at close range but lowest accuracy of any weapon type. Examples include single-barrel fast-firing weapons with larger magazines, medium-range weapons with low spread, and multi-barrel weapons with huge per-shot damage but slow rates of fire and frequent reloads.
Rifle: Versatile medium/long range weapon. Examples include accurate, high-damage semi-auto weapons, general-purpose burst or automatic rifles, and high-capacity light machine guns with heavy recoil. Special assault rifles can fire grenades or rockets with standard rifle ammunition, though at a cost of multiple rounds per shot.
Longgun: High-damage, accurate weapons which are most effective at long range, usually with very limited magazine size and slow rates of fire. They are almost always equipped with scopes, and often have a bonus to Critical Hit Damage.

Type for firearms is akin to creature type: it defines a number of variables and is often referenced by other mechanics, but alone does not tell an individual much about a firearm.

Type and Ammunition: Each type of firearm has its own type of ammunition, but ammunition is interchangeable between firearms of the same type. For instance, if you normally carry SMG ammunition and find a new SMG, your SMG ammo will fit into the new weapon (but see below).

Subtype

Firearms have three subtypes, which can be applied to any type of any complexity.

Projectile: A projectile weapon uses physical slugs to do damage.
Hybrid: A hybrid weapon uses a combination of charged energy and a physical component to deal damage.
Energy: An energy weapon uses charged energy focused through a crystal or other apparatus to deal damage.

Subtypes and Ammunition: Each type of ammunition is divided into these three categories - for instance, you could carry projectile SMG ammo, hybrid SMG ammo, and energy SMG ammo. Most firearms are constructed to only take one type of ammunition, so a standard SMG would only take projectile SMG ammo.

Firearms in Combat

This section goes over the different attack modes that firearms have.

Rates of Fire

With a modern, self-loading firearm, you can fire off several shots during the time of a typical sword swing or thrust. Pumping out a veritable cloud of lead is nothing more difficult than rapidly pulling the weapon’s trigger. To simulate this in d20 play, several new Rates of Fire have been created. Using a weapon with a special Rate of Fire lets you shoot several times with a single attack action.

Standard Fire (SF)

Standard Fire allows you to attack with a firearm as many times as you have attacks per round.

Almost every firearm permits you to perform Standard Fire. There are exceptions, though. For instance, certain Rifles and SMGs only let you fire bursts (see below).

Double Fire (DF)

Double Fire lets you fire two shots with each attack. Each shot suffers a penalty to hit equal to half the weapon’s recoil (round up, –1 minimum).

Double Fire may be directed at two separate targets. This imposes a –4 penalty to hit both targets.

Damage bonuses for specialization and the like apply to each shot you perform with Double Fire.

Triple Fire (TF)

Triple Fire lets you shoot three times with each attack. Each shot suffers a penalty to hit equal to the weapon’s recoil (-2 minimum).

Like Double Fire, Triple Fire shots may be directed at separate targets, but with a –4 Attack penalty against each target.

Damage bonuses for specialization and the like apply to each shot.

3-round Burst (B3)

A burst occurs when several bullets are rapidly and automatically fired with a single pull of a firearm’s trigger. The advantages of a Burst: it is easier to hit your target, and it is possible that you might hit your target with more than one bullet, inflicting more damage.

A 3-round Burst counts as one attack; three bullets are fired with a single pull of the trigger. If you perform a Standard Attack Action, you can do one burst. If you perform a Full Attack Action, you can perform one burst for each attack.

For every 2 + Recoil points you roll over the number needed to hit your target, an additional bullet hits and inflicts normal damage, up to the total number of bullets fired at your target. Resolve the damage of each bullet separately. (For example, if you use a Recoil 3 weapon, for every five points you roll higher than the amount needed to hit your target, another bullet hits and inflicts damage.)

You cannot hit an opponent more times than the shots in your burst. For instance, if you fire a three round burst, no more than three shots can hit your target.

You cannot direct a three round burst at multiple targets.

Damage bonuses for specialization and similar abilities apply to all the bullets in a burst, but you cannot benefit from sneak attack or other precision-based damage. Regardless of your attack roll, you cannot make a critical hit with a 3-round burst, though a roll of natural 20 indicates that all of the bullets automatically hit the target.

Point Blank Burst: If you fire at Burst at a target within 5’ and hit, all bullets in the burst automatically hit the target.

5-round Burst (B5)

In a 5-round Burst, five bullets are automatically and rapidly fired with a single pull of the trigger. A 5-round Burst works like a 3-round Burst, but you suffer a penalty to the attack roll equal to one-half the weapon's recoil, rounded up, minimum -1.

10-round Burst (B10)

A 10-round Burst is an extended burst intended to spray an area with a hail of bullets. With a single pull of the trigger (one attack), 10 rounds are automatically fired from the weapon. For all practical purposes, a 10-round burst is rock-n-roll, fully automatic fire.

10-round Bursts are treated like area-effect attacks. It affects a 5’ wide path in a straight line out the weapon’s range. Everything within that path suffers damage from the burst. A Reflex saving throw halves the damage. The DC of the saving throw is equal to your attack roll - the weapon's recoil.

The weapon inflicts double normal damage; roll two times the normal dice and double all damage modifiers. You do not apply sneak attack or other precision-based damage to a 10-round burst: you simply do not have the means to strike as accurately as possible.

You cannot make a critical hit with a 10-round burst. However, a result of a natural 20 on the attack roll increases the damage as though you had made a critical hit, using the weapon dealt by the burst as the base damage.

Example: You are using an SMG that deals 2d4 damage, with a critical multiplier of x3, and make a B10 attack. Normally this attack would deal 4d4 damage; if you roll a natural 20, however, it instead deals 12d4 damage.

Targets of a burst may apply Deflection bonuses to their AC to their Reflex save against attacks of this nature.

50-round Burst (B50)

Some self-loading fully automatic weapons are capable of 50-round bursts.

When you make a 50-round burst attack, you gain a +5 circumstance bonus to the attack roll.

A 50-round Burst is similar to a 10-round burst in mechanics, except it affects a 10’ wide path, but otherwise functions as a 10-round burst.

The weapon inflicts triple normal damage; roll three times the normal dice and triple all damage modifiers.

Firearm Modifiers

Quick section, just to get ideas on the table.

Default Firearm Chassis
Type	Dmg (S)	Dmg (M)	Critical	Type	Penetration	Recoil	Fire Rate	Range	Magazine	Qualities	BPs
Pistol	1d4	1d6	x3	P	2	2	SF	30 ft.	1	---	0
SMG	1d3	1d4	x2	P	2	2	B3	50 ft.	10	---	10
Shotgun	1d6	1d8	19-20/x2	P	0	3	SF	20 ft.	1	---	10
Rifle	1d8	1d10	x3	P	3	2	SF	60 ft.	1	---	0
Longgun	1d10	1d12	19-20/x3	P	4	1	SF	100 ft.	1	---	0

Damage +: This modification increases the damage dealt by the firearm.

Fire Rate +: This modification increases the potential fire rate of the weapon.

Melee Damage +: This modification increases the damage the firearm does when used as a melee weapon.

Penetration +: This modification increases the firearm's Penetration value (the amount of armor bonus to AC and DR it ignores).

Stability +: This modification reduces the firearm's Recoil value.

Range +: This modification increases the firearm's Range.

Magazine Size +: This modification increases the maximum amount of ammunition the firearm can hold.

Accuracy +: This modification increases the firearm's enhancement bonus to attack rolls.

Reload Speed +: This modification reduces the time required to reload the firearm, or increases the amount of ammunition that can be reloaded at a time.

Crit Damage +: This modification increases the firearm's critical range and/or multiplier.

Feats

The following are a selection of feats that are relevant to firearms.

BASIC FIREARM PROFICIENCY [General]
You are proficient with basic firearms.
Benefit: You gain proficiency with all Basic firearms, of all Types and Subtypes.

ADVANCED FIREARM PROFICIENCY [General]
You are proficient with a class of advanced firearms.
Prerequisite: Basic Firearm Proficiency, BAB +1.
Benefit: Choose a Type of Advanced firearm. You gain proficiency with all Advanced weapons of that type.
Special: You can take this feat multiple times. Each time you do, you can select a new Type.

COMPLEX FIREARM PROFICIENCY [General]
You are proficient with a subtype of complex firearms.
Prerequisite: Advanced Firearm Proficiency, BAB +1.
Benefit: Choose a Type and Subtype of Complex firearm, for a Type with which you have the Advanced Firearm Proficiency feat. You gain proficiency with all Complex weapons of that type and subtype.
Special: You can take this feat multiple times. Each time you do, you can select a new Type and Subtype.

Technology: Firearms

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