D20 “Andrew’s Firearms”

Posted by AndrewC on 4th February 2015
Posted in: D20, Game Rules.

Alternative D20 Firearm Rules

Preamble

These rules are not intended to be comprehensive – they are a replacement for any of several D20-based system’s firing modes and “recoil” systems. They are a deliberate balance between realism and complexity, and are intended to be “feat lite”, since many d20 firearm systems would render low-level soldiers largely ineffective (as well as being overly complex)!

It also includes an optional “wounds” system, and energy weapons with heat management

Note; It is fully intended that burst fire has very low accuracy, due to the number of shots you can take with it and the high damage on hits.

Actions

  • Full
  • Half
  • Free
  • 5ft Step

In any round:

  • You may take any number of free actions;
  • You may take one full or two half actions;
  • However, only one movement and one attack action per round is allowed;
  • If no movement action has been taken, the character can take a 5ft step, regardless of other actions he may have taken.

Firing modes:

Single Shot (SS): The weapon may fire once per round, as a half action.

Three-round burst (3S): This attack is a full action, and gives +2 to hit and an additional dice of damage over the usual weapon statistics. It uses three rounds, and may not be used without at least three available rounds. Alternatively, the firer can suppress a single target.

Semi-Automatic (SA): Firing a weapon in semi-automatic mode is a full action. It allows the user to make their usual number of attacks with a weapon. Alternatively, a single attack can be made as a half action. A weapon must be capable of semi-automatic fire before it can be used for attacks of opportunity. The maximum number of attacks which can be made is equal to the available rounds in the weapon. Attacks may be used to suppress single targets, but these must be made before any direct attacks.

Burst (full auto) (B(x)): Firing a weapon in bursts is a full action. The gun fires x (per-gun defined) attacks, and must have at least five times the weapon’s x value in available shots to be fired on automatic, an each increment of burst uses five rounds. Targets must be suppressed with the first attack directed at them, but additional bursts may roll standard attacks at -4 to-hit. The Burst Management feat reduces this penalty to -2. Targets attacked must be within ten feet of the previous target, and within thirty feet of the original target. Hits from burst fire do two additional dice of damage over the usual weapon statistics.

i.e. A machine gun with B(5) and recoil 4 has four targets in front of it. The firer (who has the Burst Management feat) uses one attack on each target, suppressing them. He then attacks the nearest target, at -10 to-hit (see below, recoil*2 and burst penalties). The weapon usually does 2D12 damage, with two dice added this becomes 4D12.

Suppression: Some weapon attacks suppress their targets, as do all weapons when firing in Burst mode (as above). No attack roll is needed to suppress a target, and it does not do any direct damage. A suppressed target must make a DC15 reflex save on their next action if is not defensive (diving to the ground / into cover). On a failed save, they are hit once by the weapon which was suppressing them for the weapon’s normal damage. If they pass the save, they may act, but suffer a -4 penalty to all actions. A single target can only be suppressed once by any single gun at any time, although multiple guns may suppress a target at the same time. The target never suffers worse than a -4 penalty, although it may be forced to make multiple saves.

Some weapons are better at suppressing targets than others, they may have the modifier suppression+x, which adds to the DC of the suppression save. i.e. Suppression+2 weapons should have a reflex save DC of 17. Weapons with a suppression modifier also always suppress their targets, even when not firing in Burst mode.

Recoil:

When guns fire, you suffer recoil. Recoil affects your changes to hit when you are spraying bullets all over the place. Guns have a recoil value, and each point of recoil, if not offset by “compensation” (comp), gives a -1 to-hit penalty. Recoil does not carry over between turns.

Firing mode;

  • B(x)- hit penalty = recoil*2
  • 3S – hit penalty = recoil
  • SA – hit penalty = recoil
  •  SS – no recoil = none

Stance modifiers;  (apply these first)

  • Vehicle/Building mounted: +5 comp (personal weapons only, vehicle scale weapons are +0). No other modifiers apply
  •  Holding a two-handed weapon (i.e. Rifle) in one hand creates double recoil, as well as any other applicable penalties (i.e. off-hand).
  •  Recoil is offset by compensation (comp). Certain weapon accessories give compensation, which offsets recoil penalties on a 1:1 basis. These bonuses do not stack.
  •  Holding a one-handed weapon (i.e. Pistol) in both hands: +2 comp

Other modifiers; (apply this after)

  • Bipod: +2 comp#
  • Tripod: +3 comp#
  • Recoil sling: +1-3 comp – depending on rating. Requires a strength bonus equal to the rating, or sling goes not give any benefits and a -2 penalty is suffered to-hit, regardless of the actual weapon recoil)
  • Exo-Armour mounted: +2-4 (depending on size)
  • Recoil compensation feat: +2 comp.

(#Bipods and tripods must be properly set up to use, a full action, before they give their bonus. They must be folded away, a half action, before the user moves or he will suffer a -1 penalty to comp until he either sets up or folds away the bipod/tripod)

Sample Weapons

Weapon modes recoil damage critical accuracy
Pistol SS,SA 2 2D6 19-20 0
Auto Pistol SS,SA,B2 2 2D6 20 -2
Assault Rifle SS,SA,3S,B3 3 2D8 19-20 0
Battle Rifle SS,SA,3S,B3 4 2D10 18-20 0
SMG SS,SA,B3 2 2D6 20 0
Light MG 3S,B5 4 2D12 19-20 0  suppression+2
Sniper Rifle SS 4 2D12 18-20 0
Shotgun Slug SS 2 2D10+2 19-20 0
Pellet SS 2 1D6 20 3
Autoshotgun Slug SS,3S, SA 3 2D10 19-20 0
Flechette Gun SS 1 3D10 18-20 2 (doubles DR)
  • Critical hit = +2 damage/die, automatic 1 wound/die (base dmg) (plus normal wounds!) – normal rules apply for confirming criticals
  • Electrothermal weapons – +2 to-hit, +1 recoil (use different ammunition to standard guns)

Examples

  • A man with BAB +6/+0 fires a pistol in semi-automatic mode. With recoil 2, this means his adjusted attack is +4/-2. If he was holding it in both hands, this would offset the recoil and leave him at his base BAB.
  • A man with BAB+10/+4 fires a battle rifle in semi-automatic mode. He has a bipod. Recoil is 4, minus two for the bipod. Hence, his adjusted attack is +8/+2.
  • A man with BAB+5 fires a light machine gun in burst mode. He has a tripod. Recoil is 8 (4 doubled), minus three for the tripod. Adding the -4 penalty for burst fire attacks, any attacks he makes after suppressing his targets will be at -4 (-(8-3) -4 +5)
  • A man with BAB+6/+0 fires an assault rifle with one hand in three-shot mode. Recoil is 6 (3 doubled), as it’s held one-handed. He can make a single attack which has the +2 to-hit for a 3-shot burst, for a total of +2. If it hits, it adds an additional die to the weapon’s damage for 3D8 damage.

Point-blank fire

Weapon size hit modifiers apply:

  • Small (pistol) +2
  • Medium (SMG) +0
  • Large (rifle) -4

Armour

Armour DR is usually subtracted directly from weapon damage. However, a penetrating weapon halves armour DR and a devastating weapon ignores armour DR. There may be limitations as to when these apply (i.e. “non-sealed armour”). Note that even if a hit is reduced to zero damage, it is still considered a hit for all other purposes.

Wounds

Wounds = con. Heal 1/day with medical care, or DC15 fortitude save to heal without medical care. Failing the save inflicts 1 wound damage.

Threshold = 5+con bonus+lvl/3 (FRN), suffering damage over threshold does one wound. You can suffer multiple wounds in a given hit –  i.e. if your threshold was 8 and you were hit for 20 damage, you’d suffer 2 wounds.

You should apply EITHER -1 to all actions/wound or at 50% wounds -4 to all actions, depending on your intended gameplay complexity.

  • 0 hp = unconscious
  • 0 wounds = dead

Bullet types

Bullets – (not shotguns)

  • Shatter – ceramic, made for use in space stations. Triple armour DR. (very unlikely to penetrate hulls)
  • Explosive – +1 dice damage, -2 to-hit, Fumble (1)
  • Full Metal Jacket – +2 damage, -1 crit range (weapons with a normal crit range of 20 gain no benefit from FMJ ammunition)
  • HEAP – amour penetrating, halve damage after DR
  • Hollow Point – +1 dice damage, double DR, Fumble (1), (1-2) on full auto
  • Subsonic – -5 to detect trajectory or hear gunfire, Fumble (1), -2 damage
  • Tracer – -1 damage, can set things on fire, +2 offset to to-hit penalties in low light/night conditions. Illuminates firer.

Special Shells (shotguns)

  •  Dragonbreath – flamer. Fumble (1-3). Fumbles always damage the gun, causing it to be unusable until repaired.
  • Gas – Contains a gas. Fumble (1-2). Fumbles always shatter the shell in the gun. (user is affected, if the gas has a radius this is applied normally as well)
  • Flashbang – DR15 check or stuns for 1D3 rounds. Save disorientates for 1 round.

Sights

  • Optical – x2 range modifier
  • Laser – x1.5 range modifier, +2 to-hit. May trigger laser warning detectors.
  • Thermal – x1.5 range modifier in the dark versus enemies emitting detectable heat (living, non-sealed armour).
  • Low-Light – x1.5 range modifier, no low-light penalties.

Fumbles and critical fumbles

Some types of ammunition are jam-prone or otherwise risky to fire. If you roll a fumble, roll the D20 again – if you roll another fumble, it is confirmed as a critical fumble instead. Fumbles jam the weapon, ruining the rest of the clip (if any) and requiring a full round and a DC15 tech (projectile weapons) roll to clear. A critical fumble will be decided by the GM, but can include weapon explosions, hitting allies, setting things on fire, bringing down walls in a bad place, etc.

(Note; Energy weapons have somewhat different fumble rules)

 

Energy Weapons:

Unlike projectile weapons, energy guns don’t have any recoil. However, they can overheat, potentially injuring the user, if fired too rapidly. They can be extremely hazardous when used for burst fire remembering that each burst is considered five rounds – while they can do greater damage than projectile weapons, they are less suited to suppressive and sustained fire.

Each shot of an energy generates one heat, unless otherwise noted (plasma weapons generate two heat per shot, for example). Weapons remove their dispersion value from this during an attack action, and again at the end of any turn in which they are not fired – this is typically two for a pistol and three for a rifle. For each point of heat, which is calculated before the attack, the weapon gains a point of Fumble. For example, a weapon with heat 3 would have a fumble value of (1-3).

i.e. a Laser Rifle with a dispersion of of 3 has fire modes of SS,SA and Burst2.

It does 4D6 damage per-shot. Therefore, firing the weapon in burst mode means 10 shots, or a heat of 10; 7 after dispersion. This means there is a fumble value of (1-7).

If the initial roll is a fumble, regardless if it is confirmed or not, this may render the weapon power pack worthless until repaired and recharged. This occurs if the user fails a Tech(Energy Weapons) check with a DC of 10+heat. The usual rules for a critical fumble do not apply to energy weapons; They confirm critical fumbles only on a second roll of 1.

i.e. The above laser rifle, on burst fire, would have a DC of 17 to avoid this failure.

Weapons may not go above 20 heat.

Weapon modes dispersion damage crit accuracy
Laser Rifle SS,SA,3S,B2 3 4D6 19-20 2
Particle Rifle SS,SA,3S 3 3D8 18-20 0
Plasma Rifle SS, SA 4 4D10 19-20 -1
Sonic Rifle SS,SA 2 1 20 -2

Heat dispersion adjustments;

  •  Coolant backpack: +2, or +5 for one round as a free action, but reduce the permanent bonus by +1 (to a minimum of +0, when this may no longer be done)
  • Heat dump: +4, one-use
  • Exo-Armour Mount: +50% (FRD) – also, may have coolant “backpack” to +3 normal maximum
  • Vehicle/Building Mount: +75% (FRD) – also, may have coolant “backpack” to +4 normal maximum
  • Oversized cooling fins: +1, but -2 to-hit
  • Heat management feat: +1

Weapon types;

  • Laser: armour penetrating
  • Particle: plus 1 EMP damage/die
  • Plasma: armour devastating vs non-sealed armor, -4 to-hit per range increment not -2, 2 heat/shot.
  • Sonic: Require a DC18 fortitude save, failing the save renders the target stunned for 1D4 rounds. Failing a second save while stunned knocks the target out. Crit is DC22 save.

(note – starship point defence weapons are burst-fire vehicle scale weapons).

—-

These Rules are released under the Open Gaming Licence 1.0a
Designation of Open Content: All except Preamble, which is Product Identity