OSR Firearms Rules

NOTE: 4.4.2019

Edits to quality of writing and making the language more clear.

Change the range of possible extra targets hit on Autofire: Rock and Roll from 5' to 10'.

The basics if inserting firearms into my games.
Stats for basic firearms will be posted separately by era (Colonial, Victorian/Western, Pulp, Modern.)

Initiative
Normal combat initiative is 1d6 + Dex bonus.
 
Drawing a Weapon
A character can draw a weapon and use it in the same round but with a penalty of -3 to the initiative roll and a -2 to the attack roll. This can be further modified by equipment bonus or penalty and character ability such as the Gunfighter fast draw ability.

Example:
A character has a +1 Dex bonus and is using a pocket pistol for an additional +1. He rolls a 5 on his initiative -3 for pulling a weapon in the same round +2 for bonuses for a total of 4 on initiative.

Equipment Initiative Modifiers for Drawing a Weapon (-3 to initiative)
These bonuses/penalties only apply when Drawing a weapon, not normal initiative.
Derringer or Pocket Pistol +1
Heavy Pistol, Carbine, Sawed Shotgun, Coach Gun -1
Heavy Carbine, Rifles, Shotguns -2
Short Barrel +1, extra –1 to range penalties
Long Barrel -1, increase range increment by fifty percent
Flap/Army Holster -1
Swivel Rig +1, -1 to hit, must unhook to reload
Spring-sleeve Holster +1

Rate of Fire
Normal Attack
Anyone can make one attack per round with no penalty. The basic careful shot.

Single Action Pistols
The shooter can make two attacks with a -3 penalty per shot.

Semi-Auto and Double Action
The shooter can take two shots per round with a –2 per shot.

Bolt-Action
The rifle can be fired twice per round with a -3 penalty per shot.

Fan the Hammer/Flick the Lever
Holding down on the trigger and fanning the hammer of a single-action revolver with your off hand or quickly flicking the lever and pulling the trigger of a lever-action carbine or rifle to fire rapidly.
3 attacks, -4 per attack.

 Automatic Fire
This is an abstract system. Auto-fire is tricky and not precise with lots of wasted ammo.  Lots of bullets fired will give opportunities for more attacks and possible damage at the cost of accuracy. Rolling thirty attacks and thirty damage dice is, frankly, a bore and not what I want to emulate in a game system.

Firing this amount of ammo from a hand-held firearm makes controlling the weapon difficult when it is spitting out 10+ rounds per second. Penalties are applied to hit. The trade-off of this is the opportunity for more attacks even at a penalty.

Controlled Bursts
This option has the shooter preserving accuracy and ammunition by only squeezing the trigger for short controlled bursts of automatic fire.
⦁ Three attacks are allowed with a penalty of -2 penalty per attack.
⦁ An extra damage dice of the firearm's damage type is added to damage rolls.
⦁ Five bullets are used per attack.

Rock and Roll Full Auto (Suppressive Fire)
This option is used when attempting to hit a number of targets grouped together or causing them to keep their heads down with suppressing fire. Accuracy and ammunition is the price for this.
⦁ Three attacks are allowed with a penalty of -4 penalty per attack.
⦁ An extra damage dice of the firearm's damage type is added to damage rolls.
⦁ Ten bullets are used per attack.
⦁ This option also has a chance of hitting more than one target per attack. Up to two more targets can be targeted as long as they are within 10' of the primary target. One attack roll is made and compared to the AC of each available target of the attack. Auto-fire damage is rolled for each target hit.

A bi-pod, tripod, or mount  drops the accuracy penalty by half.

3-Round Burst
Modern weapons frequently come with the option of a preset number of rounds in burst fire for a weapon. This is to save wasted ammunition and improve accuracy. Typically the attack uses 3 bullets in the burst per pull of the trigger.
⦁ The attack is at a +1 bonus to hit. If hit by five or more one extra damage dice is added.
⦁ Two attacks can be made per round but at a total penalty of -1 per attack.

Automatic fire is lethal. Watch yourself.

Range
Firearms have ten range increments, and suffer a  –2 penalty per increment after the first.
Point Blank: Within 10' of a target (5' for derringers) the shooter gains a +4 bonus to hit.

Firearms Vs Armor
Pistols and Longarms are effective vs armor at close range and reduce the effectiveness of the armor's AC bonus. This applies only to that portion of the character's Armor Class that comes from wearing armor and shields; Dexterity bonuses are unaffected as are cover bonuses. The penalty cannot make a character's Armor Class worse than if he was wearing no armor.

Pistols (this includes carbines, repeating rifles, etc that used pistol ammunition)
At the first range increment pistols ignore three points of armor, at second pistols ignore two points, at third pistols ignore one point. Beyond this no armor is ignored.

Longarms (this includes rifles, shotguns, etc that used rifle and heavy ammunition.)
At the first range increment longarms ignore five points of armor, at second longarms ignore three points, at third longarms two points, at fourth longarms ignore one point. Beyond this no armor is ignored.

For creatures, if the DM decides that their AC includes natural armor, the firearm would ignore it as well. If you're unsure of how much to ignore removing 2 points of creature AC is a good rule of thumb. Remove more if you feel you should.

Reloading
Firearms which require a magazine, clipper strip, strip, etc take only one round to reload and ready. However a desperate shooter can hurry the reload and attack with a –2 penalty to his attacks that round.

Non-magazine weapons (revolvers and rifles with internal magazines for example) can only reload a maximum of three bullets per round. No other action except movement can be attempted while reloading. However, a shooter can, if desperate, reload one shell and attack with a –4 penalty for rushing the attack.

A single shot weapon (break open, bolt action, etc.) requires a full round to reload.

A muzzle loading weapon takes two rounds, fire on the third.
Any action other than walking requires a Dex check otherwise the reload fails and must be started again,

Aiming with Firearms
Take a round, gain a +2 bonus to one shot. The attacker can do this for two rounds (no more) for a +4 bonus to hit.

Basic Accessories
Bipod
Reduces autofire penalty by one point for machineguns.

Telescopic Sight
The telescopic sight gives a +2 to +4 bonus to hit depending on strength and quality of the scope.
This stacks with the aiming rules.

Two Weapons
-2 penalty primary hand, -4 off hand.
You can use the multiple attack options with this. Example: firing two double action pistols twice.
-2 for each shot is added to the Two Weapon penalties for a total of -4 primary/-6 secondary with a total of four shots.
This is reduced with Point Blank fire (see under Range above.)