In a game with access to a broad range of technology, it’s likely that bows, rifles, and lasers will all employed on the battlefield. Firearms resembling those used in the modern day are relatively common, because they are fairly simple machines. There are a variety of rules in different D20 systems for handling guns and other firearms; I’ve attempted to adapt the best ones with balance in mind.
Attacks: attacks with guns are made against normal AC, not touch AC. This is due to changes in the way Armor works, and to create a more balanced playing field for melee and ranged classes.
Recoil: Powerful ballistic weapons have a powerful kick when fired. If the damage bonus from a gun exceeds your strength bonus, subtract the difference as a penalty to your attack roll.
Firing from braced/prone/mounted positions
- Braced: This firing position is similar to kneeling. Braced shots gain a 2 to AC versus ranged attacks) while making yourself easier for melee opponents to smash (-2 to AC versus melee attacks). If you want to move while braced (basically remain crouched), you move at half speed. Assuming a braced position is a free action; standing from a braced or crouched position is a move-equivalent action that does not provoke attacks of opportunity.
- Prone: This firing position gives a +2 circumstance bonus to attacks with guns.
*Tripod or mounted gun: You gain a +2 circumstance bonus to attack with guns mounted on tripods or fixed in place.
- Mounted: Firing from a mount or moving vehicle is penalized in Pathfinder if your mount/vehicle moves more than its base move speed. Double move is -4 to attacks, and Run is -8 to attacks.
Loading: Most PL4 and 5 guns require a move or swift action to load. Earlier PL guns often require a standard or full round action. More advanced weapons may require unusual ammunition or power packs, but will generally also require only a move or swift action to reload. Reloading a gun without the training to use that weapon increases the misfire chance by 4 (this is not cumulative) and takes a full round. Loading any gun provokes attacks of opportunity.
Misfire: Since guns are machines or devices of some sort, they can malfunction. Since they are dangerous devices, the malfunctions can be dangerous as well. “If the natural result of your attack roll falls within a firearm’s misfire value, that shot misses, even if you would have otherwise hit the target. When a firearm misfires, it gains the broken condition. While it has the broken condition, it suffers the normal disadvantages that broken weapons do, and its misfire value increases by 4 unless the wielder has training in the particular type of firearm. In that case, the misfire value increases by 2 instead of 4.” Pathfinder SRD, Firearms.
Broken firearms from PL3 will explode if they misfire again (see Pathfinder Firearms link), while firearms from PL4 and 5 will simply misfire again, raising the misfire chance further. More advanced weapons may react unpredictably to a misfire. Typically, PL4 and PL5 guns in good condition only misfire on a roll of 1 (rarely 1-2); PL3 firearms misfires are sometimes higher (see above link). More advanced weaponry, often having been through hundreds or thousands of years of wear, may have elevated misfire chances from the start, and should be handled with considerable caution by experienced teknicians.
Auto and burst fire: many guns are made to fire rapidly, far more rapidly than a trained archer can fire a bow. There are two systems for handling this in Aeons.
- Burst fire: Many guns have the ability to fire short bursts at single targets instead of simply single shots. Without special training, firing in burst mode for most weapons results in an attack penalty of -8 (due to recoil) for three shot bursts or -10 for five shot bursts. Three shot bursts deal one extra die of damage untrained, while five shot bursts deal two extra dice untrained. These attack penalties stack with the -4 penalty for untrained use.
- Auto fire: Guns capable of fully automatic firing can be used to spray shots into a 10ft by 10ft area, requiring 10 shots be expended. Hitting the area requires an attack roll to hit AC 10. Targets in the area must make a Reflex Save with DC equal to the attack roll or take the weapon’s damage. Those who save avoid all damage. Without the Advanced Firearms Proficiency feat, the attack roll receives a -4 penalty, which stacks with the untrained penalty.
Note that some guns from more advanced Progress Levels will reduce the penalties for autofire, as they have reduced or no recoil. These firearms operate with less obvious principles, however, and may be more difficult to use overall due to their complexity. Many have on-board targeting assistance, guided munitions, gyroscopes, or other features requiring Knowledge (Tek) to use.
Basic Firearms Proficiency
Benefit: The character can fire firearms from Progress Level 3 through 5 with no penalty.
Normal: Characters without this feat take a –4 penalty on attack rolls made with firearms from these Progress Levels, and nonproficient characters who load such firearms increase all misfire values by 4 for the shots loaded.
Note: Gunslingers and Kaiguns receive Basic Firearms Proficiency as a bonus feat at first level.
Advanced Firearms Proficiency
Prerequisite: Basic Firearms Proficiency
Benefit: The character use autofire without penalty. Burst fire attacks are made at -6 for 3 shot bursts and -8 for 5 shot bursts.
Normal: Characters without this feat take a –4 penalty on autofire attack rolls, and -8 or -10 on burst fire attacks.
Prerequisite: Wisdom 13, Dexterity 13, Basic Firearms Proficiency, Advanced Firearms Proficiency
Benefit: The penalty for firing bursts is reduced to -4 for 3 shot bursts and -6 for 5 shot bursts, and bursts deal one more die of damage (2 dice for 3 shot bursts, 3 for 5 shot bursts).
Exotic Firearms Proficiency
Prerequisite: Intelligence 13, 5 or more ranks in Knowledge (Tek), Basic Firearms Proficiency
Benefit: You can attempt to use guns from higher Progress Levels (6+) without penalty. You may still need to make a Knowledge (Tek) roll to use any advanced features of a weapon.
Normal: Characters without this feat have a -4 penalty to attack with exotic firearms. That penalty stacks with the untrained penalty for characters without Basic Firearms Proficiency.