Simplified HMS APOLLYON or OD&D gun rules.

Below are draft rules for firearms that I would use for HMS APOLLYON or any similar reasonably high lethality game based on a Basic/Expert or more specifically OD&D (whitebox) system.  I have only dealt with small arms below, but crew served weapons such as heavy machine guns and artillery have their own, very deadly, rules that I will detail in a future post.

My aim is to make firearm rules that provide some advantages to guns, but limit them in other ways so they don't come to dominate player's weaponry.

GENERAL RULES

Small arms are generally treated similarly to bows and crossbows, but provide several advantages.  The most general of these is exploding damage.  Unlike traditional weapons, firearms are relatively easy to use effectively, and may by fielded by any class without restriction which provides a huge advantage to less martial classes. Secondly, guns are capable of doing large amounts of damage on a lucky shot, and all firearms, including automatic weapons, have the ability to do exploding damage, causing an additional die of damage when they hit for their maximum damage, and continues to accrue with every roll of maximum damage.

Generally in an OD&D system, all firearms do 1D6 per bullet, though rare weapons do either multiple die of damage or have modifiers.  

Example: A rifle attacker hit and rolls a nature “6” on their “D6” damage.  The player rolls again for damage and adds it to the “6”.  If by rare chance the shooter rolls a second “6” an further die of damage is rolled and added. This accumulation of damage continues until a number less then maximum damage is rolled.

Burst: is another concept that separates firearms from other D&D weapons.  Some firearms can shoot multiple bullets quickly.  While fully automatic weapons and shotguns are treated differently (see cover below), even revolvers can be fired as a burst.  Burst weapons can strike multiple times up to the burst value in a single attack but use a larger number of bullets to do so.  A weapon fired as a burst rolls attack normally, but for every '2' pips above the number needed to hit strikes with an additional bullet.  Thus if a gunman firing an automatic with a burst value of 3 and rolls a 18 against and target which requires a 12 to hit, all three shots in the burst hit (12-18 = 6, so first shot hits on 12, second on 14 and third on 16) each doing damage.  Bursts expend large amounts of ammunition however, using 2x burst value -1 rounds of ammunition. Thus a revolver with 'burst 2' uses 3 rounds per shot. Most burst weapons may be fired as a single shot as well.

Cover: Automatic weapons, such as assault rifles and submachine guns, are weapons with a magazine of over 12 and the ability to exhaust that magazine in a single round of fire.  Automatic fire is very effective, but empties the weapon, and targets are often hit with multiple bullets, ricochets and fragments.  No attack roll is made against automatic fire, instead the target makes a saving throw vs. wands (or devices). On a failed save the target takes normal(if a shotgun) or double(if an automatic weapon) damage for the gun , and on a success 1/2 damage.  Shotguns likewise attack a single target's saving throw rather than armor class.  The only protection against automatic weapon attacks is cover, not full cover (which is presumed to prevent attack with ranged weapons) but any cover, even easily shredded items such as furniture or partial protection like a corner to peer and fire around.  Even diving to the ground and remaining prone will provide sufficient cover to alleviate automatic weapon damage. Such cover normally gives the attacker a -2 to -4 to hit, but against automatic and shotgun fire it reduces damage. A target of an automatic weapon attack who elects to take cover (and they may do so at the time of the attack, unless surprised, in lieu of a future action) will take 1/2 damage is they fail the save, and no damage on a success.

Example: Spotting a pack of five skulking Merrowmen, Steward Sargent Clotho picks one and blasts away with his double barreled shotgun.  The little eel man is not surprised, some feral sense of danger warning it, and throws itself to the ground, taking cover.  Despite taking cover the Merrowman fails it's save against wands, taking 1D6/2 points of damage from the blast.  The rest of the Merrowmen charge Clotho eschewing cover, and he has a chance to blast another before the creatures are upon him.  The second shot hits the lead Merrowman cleanly, doing 1D6 damage.  Unfortunately for Clotho there are now three Merrowmen in melee with him, and he is armed with an improvised club.  Worse the wounded Merrowman has gotten off the floor and is preparing to join its companions the next round.

Note: If using distinctive weapon v. armor type rules, firearms treat armor as if it were one category of armor worse (light armor is treated as none, medium as light and heavy as medium).

Note: If using strict encumbrance rules (such as STR = encumbrance) a box of cartridges or clip is deemed an encumbering item.  For black powder weapons these numbers tend to be high (50 bullets), but a powder horn must also be carried as an additional encumbering item.  For shotguns the number of cartridges per encumbrance point tends to be low, usually 12.

SPECIFIC FIREARM TYPES

Pistols: Useful weapons at range, but inaccurate, all pistols suffer a -1 to hit at any range beyond 50’ (though normal aiming bonuses apply).  Pistols have the advantage of being usable in melee combat effectively.  On the first round of melee combat pistols may be fired as normal without any loss of effectiveness.  On subsequent rounds however the pistol is not as effective a weapon, and while they may be fired without penalty to attack (including no firing into melee penalty) they lack the parrying ability of more traditional melee weapons.  A character using a pistol in melee after the first round suffers a two point penalty on armor class.

Wielding pistols in company with a melee weapon is also somewhat effective, and paired with a sword or other weapon (not a shield) the AC penalty may be avoided and the character may attack with either pistol or weapon.  No bonus for dual wielding applies while wielding a pistol however.

Dual wielding pistols can be effective in providing additional attacks, but presents difficulty aiming.  A -2 to hit with the first shot and a -4 to hit with the second shot.  With automatic weapons this penalty increases by an additional -1 for every value of "burst" the weapon has.

Black Powder Pistols: Single shot weapons, useful because they allow a dangerous initial attack in the first round of melee combat.  Like all muzzle loaded weapons they require three rounds to reload.  Blackpowder pistols tend to be of a heavier construction than more advanced weapons and some can be equipped with blades or even built into melee weapons eliminating any penalty for using them in melee.

Derringers: Either black powder or cartridge based these small pistols are only effective in melee combat, and generally do less damage (1D6-2 - with damage still exploding on a roll of '6') but they can be concealed quite easily.

Revolvers: Most often a cartridge based weapon, revolvers can fire multiple shots and have a burst value of '2'.  Most revolvers have six round cylinders, but like all cartridge based weapons they require 2 rounds to reload, even with a prepared 'quick-loader'.

Automatics: Automatic pistols, including submachine guns, are clip loaded, and can have high burst values and large magazine capacities. some may even be fired on full automatic, emptying their magazine in a single round and requiring a save to avoid or reduce damage.  As with other clip loaded weapons, automatic pistols take 1 round to reload.

Longarms: Longarms of various kinds, including muskets and rifled muskets, are weapons that are meant to be used at range.  Because of their size they are difficult to use in melee as anything other than an ungainly club (-1 to hit doing 2d6 take the lowest roll - as any other improvised weapon).

Bayonets:  Bayonets make a longarm far more useful in melee combat, effectively turning the rifle into a spear (Normal damage and chance to hit).  Unfortunately, fixed bayonets make aiming the rifle more difficult, causing a -2 to all ranged attacks.  Fixing a bayonet takes 1 round.

Muskets: Harquebuses, Fusils, Jezzails, or any other muzzle loading longarm, are effective either in a massed volley or if in the hands of an expert carefully aimed from a distance.  These weapons aren’t much more effective then heavy crossbows, and share the arbalest’s long loading time.  It takes three rounds to reload a muzzle loading firearm.

Cartridge Rifles: Most commonly Bolt action rifles using block, tube or strip magazines, though some must be reloaded each round between shots.  Cartridge rifles (even the bolt action ones) can be fired fairly quickly, and have a burst value of 2, though their smaller magazines mean this is not always desirable (the Steward standard issue rifle has only a five round block magazine, meaning it cannot be fire a burst more then once without reloading).  All cartridge rifles tend to be accurate at longer ranges, and suffer no to hit penalty for firing at even extreme range.  Block, tube, and strip rifles require two rounds to reload.  Rare Semiautomatic rifles exist that fire from slightly larger clip magazines, and require only a single round to load.

Scoped Rifles: Either specially designed as sniper weapons or simple military rifles augmented by optics, scoped rifles have great advantages when striking from concealment.  Using a scope is an exacting process and most effective with preparation.  Scopes remove any penalty from firing a rifle from long or extreme range, and add a bonus of +1 to hit per round (in addition to the initial round’s +4 to hit up to +10 for a ½ turn of aiming).  These aimed shorts have the unique advantage as using the bonus toward determining a critical hit.  That is, any roll that when added to the aiming bonus is greater than 20 will strike as a critical hit.  Additionally, a scoped rifle shot against a target that is not in combat (unexpected and from concealment) which hits will instantly kill any humanoid target or any target under the HD of the shooter. Even if it fails to kill such shots will do double damage and take full advantage of any backstab ability possessed by the shooter.

Sniper rifles are a subset of scoped weapons, generally capable of greater damage – doing 2D6 (or even 2D6 +1 per die) exploding damage rather than the 1D6 typical to regular rifles. These weapons are near useless a any range closer than long however, as they are unwieldy, hard to aim without use of the scope, and strike at -4 to hit.  

Automatic Rifles:  Automatic rifles are longarms that are fully automatic, and generally have large magazine capacities over 12 rounds.  They are usually loaded by clip (1 round loading time), though some have tube or block magazines (2 round loading times).  If fired in a burst they act as semi-automatic weapons (with a burst value of two - four, consuming three - seven rounds).  If fired on full automatic these weapons exhaust their entire magazine in a single round, but act as a light machine gun, targeting a single creature and automatically hitting for double (usually 2D6) normal damage.  A save is allowed vs. wands for any target, and if the target succeeds the target takes ½ damage.  Targets in cover take no damage on a successful save, and ½ damage on a failed save.

Shotguns: Shotguns never require a to hit roll, even though they fire a single round per turn.  Shotguns act like automatic weapons, targeting a single opponent and necessitating a save vs. wands.  Failure means that the target takes full damage from the weapon (not the double damage from an automatic weapon) and success means 1/2 damage.  Cover provides full protection on a save, and 1/2 damage on a failed save.  Shotguns have limited range and can only be used effectively at under 120' (or medium range/3 rounds out from melee for normal movement rate in game terms).

Solid Slugs may be fired from shotguns, making them effectively long arms, giving them double normal range.

Pepperboxes: extremely close range weapons resembling pistols that fire multiple bullets (either from separate barrels or a single barrel stuffed with bullets).  These weapons cannot be used effectively (-4 to hit outside melee range), except in the first round of melee combat, but can be devastating in close quarters require a single target to save vs. breath weapons or take full damage.  Sawed off shotguns and coach guns, as well as the traditional gambler's pepper box pistol fall into this category.

Cartridge Shotguns:  One of the more common types of advanced firearms, these weapons are most often single or double barreled break open weapons that require reloading after every shot (or two).  Reloading these weapons takes two rounds.

Automatic Shotguns: Pump or drum fed shotguns are rare, and have magazines of up 5 to 20 rounds.  they are identical to shotguns, except that they need not be reloaded as often, and drum loaded shotguns take only 1 round to reload.