Expanded 40mm Grenade Launcher and Grenade Rules for Unisystem Games
By Michael Dowell

This article presents a great deal of detail on 40mm grenade launchers, and adds some new rules for those weapons. It will certain give any character with a passion for explosions good bang for the buck. It also provides optional rules for determining the effect of wind on the various grenade types.

The Weapons
There are currently (as of January 2001) two 40mm grenade launchers in the U.S. military arsenal: the M203 and M79. 

The M203 grenade launcher is a lightweight, single-shot, breech-loaded, pump-action (sliding barrel), shoulder-fired (whew!) weapon which must be attached to a M16, M16A1 or M16A2 rifle. It is used primarily as a support weapon to cover direct line of sight gaps (caused by intervening terrain or other battlefield conditions) with indirect fire.

The M203 is supplied as a kit, and can be attached easily to M16, M16A1 or M16A2 rifles with a successful Craft (Weapon Smith or Gunsmith) skill check. First, the rifle's barrel shrouds must be removed, and the M203 mounted via integral brackets. The twin barrel shrouds are discarded, and replaced with a single barrel cover assembly (supplied with the kit), which has an integral front-mounted "leaf" sight, used for quick suppressive fire. A second, more accurate "quadrant" sight is attached to the M16's carrying handle. This sight is used when precision shots are required (or the grenadier has time to aim). The quadrant sight, when used properly, grants a +3 bonus to hit a target, but using it delays the grenadier's action to the end of the Turn (and may not be combined with regular aiming; see WitchCraft, p. 135).

The M79 grenade launcher is a lightweight, single-shot, breech-loaded, shoulder-fired weapon. It is an earlier, stand-alone version of the M203 equipped with an integral grip, folding stock and "leaf" sight (no quadrant sight can be attached to this weapon).

Both weapons are capable of firing any of the various grenade types listed below. Both weapons have a kick about equal to that of a 12-gauge shotgun, and thus are capable of injuring (bruising) an unprepared grenadier. A simple Constitution check must be passed if either weapon is fired one-handed; failure indicates a sprained (or broken) wrist (d8 Life Points which may not be healed until d6 weeks pass, not including metaphysical healing). Each 40mm grenade weighs approximately 0.5 lb. (0.23 kg).

The Ammo
There are a large variety of 40mm grenades available to the grenadier. Each has differing uses, but the distinctions between certain types are minimal at best. Several of the grenade types have an "A" designation (such as the M379/M379A Bounding Fragmentation grenades). In this case, the "A" versions represent improved ordnance. This usually means that the original (non- "A" series) ammunition had some minor but correctable flaw. Active duty military personnel are usually issued "A" series rounds, while reserves and National Guard personnel receive the original types. Below is a short summary of the different grenade types.

M781 - Training Marker: A marksmanship training aid that contains no explosives, only a powdered orange dye that is expelled on impact. The cloud of dye powder settles over an area roughly the same size as the explosion radius of an explosive grenade.

M407A1 - Practice Explosive: A marksmanship training aid that contains explosives. This grenade is used during live fire training exercises, typically in a firing range, and contains less explosive than a regular grenade. Still, it remains a dangerous to anyone around it when it explodes.

M576 - Multipurpose: A moderately common round with multiple potential uses, the M576 is a buckshot-loaded grenade. This makes it the equivalent of a sawn-off 40mm shotgun -- wide spread, high penetration (for buckshot) and thus a very high damage capacity -- at short range. The multipurpose round is not a typical "explosive" grenade -- it is, for all intents and purposes, a really big shotgun shell.

M651 - CS Gas: CS gas is a type of tear gas (a non-persistent choking agent) that is classified as a Corrosive poison (see WitchCraft, p. 140). This particular chemical agent is considered "non-lethal" and is commonly used by police to break up riots. One Turn (1-5 seconds) of exposure counts as one dose of corrosive poison. One dose or single exposure to the gas causes extreme irritation and burning in the eyes, nose, and throat. Extended exposure causes excessive tearing (watering eyes), runny nose, coughing, and often vomiting. The affected area will remain contaminated until the gas is dispersed, and the worst symptoms persist for about 15 minutes after the last exposure. CS gas can be easily dispersed by a strong wind, and is subject to the normal displacement and dispersal rules (see below).

M379/M379A - Bounding Fragmentation: This grenade is fairly uncommon. It is designed specifically for use against small (squad-sized) infantry formations. The grenade is designed to "bounce" 1 to 3 meters into the air (via a light explosive) and then explode, peppering personnel within the blast area with high-velocity shrapnel.

M433 - Dual Purpose: This is one of the more commonly encountered 40mm grenade types. It is designed to be effective against both infantry and light armored vehicles (such as the UP-HMMWV or "hummer"). It has both a high explosive charge and fragmentation wire, but is not as effective against either of its intended targets as a more specialized round.

M381 - Offensive HE: One of the two most commonly encountered high explosive (HE) rounds, this grenade has a slightly reduced blast radius, and is designed for use against infantry within shorter ranges. It is most effective when used against a static target, such as a light vehicle or defensive fighting position (or DFP, such as a foxhole).

M406 - Defensive HEAP: The M406 grenade is designed for use primarily against light armored vehicles. It has a larger blast radius than the M441, and thus is suitable for moving targets. The grenade contains an armor piercing (AP) shrapnel core capable of penetrating light armors, such as is found on the UP-HMMWV.

M386 - Defensive HE: The second of the most commonly encountered HE rounds, the M386 has a larger blast radius than the M381. This grenade is most effective when used in quantity to cover large "dead fire" zone where direct fire weapons cannot reach (ravines, ditches, etc.) or against moving infantry targets.

M441 - Offensive HEAP: The M441 grenade is used primarily against static, lightly armored targets (such as sandbagged DFPs or light bunkers). It has a smaller blast radius than the M406, and thus can be used at shorter ranges.

M585 - Star Cluster: This grenade fires a cluster of five small magnesium flares that burn with an intense white light. The flares reach an altitude of about 150m before beginning their descent. The star cluster grenade is mostly used defensively to blind enemies during nighttime combat by destroying their natural night vision and overloading their low-light (starlight) scopes and goggles, as its hang-time is short. The M585 Star Cluster flare grenade only displaces about half as far laterally as other signal grenade types, loses almost no launch altitude -- the flare is small and produces little wind resistance -- and is subject to the dispersal rules below. Burning magnesium flares inflicts D8x5(20) damage per second if touched, and are also hot enough to melt through sheet metal.

M583/M583A, M661, M662 - Star Parachute: The Star Parachute grenades come in a variety of colors, and are used to illuminate areas of a nighttime battlefield and mark enemy locations. The grenade reaches an altitude of about 150 meters, whereupon its attached parachute opens and it begins to descend. The Star Parachute comes in three colors (white/white, green and red, respectively) and can also be used for signaling. Star Parachute grenades are only slightly displaced by wind (about half as far) during launch - that is, before the parachute opens - and are not subject to dispersal. After the 'chute is opened (when they reach about 490'/150 m high) Star Parachute grenades suffer from the same lateral downwind displacement as smoke and gas grenades. A burning magnesium flare will inflict D8x5(20) damage per second if touched.

M676, M680, M682 - Smoke Canopy: Smoke canopy grenades are used defensively to provide cover for advancing troops. They produce a large cloud of colored smoke that obscures vision and most forms of visual enhancement (low-light/starlight scopes/goggles, thermal imagers, etc.). The smoke is almost completely non-toxic, but causes the same effects as any other types of smoke (watery eyes, coughing, etc.) if inhaled in quantity. Smoke Canopy grenade clouds displace laterally in wind as normal, but the height of the cloud is only subject to about half the normal displacement. An actively smoking grenade will inflict D8(4) points of burn damage if touched.

M713, M715, M716 - Smoke Marker: Smoke Marker grenades are similar to Smoke Canopy grenades, except that they are designed to produce a column of smoke rather than a billowing cloud (although this distinction can become moot in a high wind). They are used mostly as daytime markers and for signaling, and come in three colors (red, green and yellow, respectively). Smoke Marker grenades are subject to all the displacement and dispersal rules below. An actively smoking grenade inflicts D8(4) points of burn damage to anyone touching it.

Below are tables with the suggested values for integrating these grenades into the Unisystem rules.

Current U.S. 40mm Grenade Launchers Table

*Loaded weight, with 30-round magazine. These weights may seem a bit off; however, because of the parts swap during installation (mentioned above), they are correct.

Current U.S. 40mm Grenades Table

* The term "ogive" is derived from the name for the curved forward tip of a missile or rocket (a military term, which are often somewhat archaic). Ogive specifically refers to the curved nose of certain grenades -- this part is analogous to the slug component of a bullet, and contains the functional (i.e., explosive, flare, etc.) "warhead" of the grenade. On some grenades, only the forward ¼" of the ogive -- the tip -- is colored or marked. On other grenades, the entire ogive is colored, and the use of this term is meant to differentiate between the two.

Blast Radius And Damage Values Table

* CS (Tear) gas is a Corrosive poison; it is considered Strength 6 to resist, but only Strength 1 for damage purposes. The grenade emits a cloud of gas with an effective radius of 100m in calm conditions.

† In clear, ideal conditions flares produce enough light to illuminate a 500-yard/meter radius. They also produce enough heat to spontaneously ignite fires, and to produce severe burn damage if touched while lit.

‡ Smoke grenades also produce enough heat to spontaneously ignite fires, and inflict moderate burn damage if touched.

Optional Rules - The Effect of Wind Speed on Grenades

The optional rules provided here are intended as guidelines, and for simplicity's sake do not take into account other weather factors like ambient temperature, up/downdrafts, humidity and precipitation, etc. A quick wind speed displacement reference table is also included at the end of this article.

Wind causes smoke and gas clouds (as generated by grenades) and grenade-type flares to move beyond the original target zone. This is called displacement. The amount of smoke or gas displacement is relatively easy to gauge. For each mile per hour (mph) of speed the wind has, the cloud displaces about 1.5 foot per second downwind, and for each kilometer per hour (kph) of speed, the cloud displace 0.3 meters per second downwind. (Refer to the table below for specific values.) A cloud of gas or smoke also normally loses one unit (foot, meter) of altitude for every unit of lateral (horizontal) displacement.

Winds also cause clouds of smoke, gas and star cluster grenades to thin or spread out the further they get from their point of origin. This is called dispersal. The effect of dispersal is a reduction in the effectiveness of the smoke or gas cloud or cluster flare as it spreads across a wider and wider area. Smoke and flare grenades normally lose half their density, visibility or obscuring value for every 250 feet (75m) they are displaced. This dispersal is continuous and cumulative for as long as the wind blows -- at 500 feet (150m) of total displacement distance, a smoke cloud would be at one-quarter effectiveness, and so on. CS tear gas clouds become Strength 3/1 at 165 feet (50m) and Strength 1/1 at 330 feet (100m) displacement. Beyond 350 feet (110m), they are almost completely ineffective.

Smoke grenades burn for 2D6(6) minutes. Flares remain airborne for 2D6(6) minutes, but only burn for 2D4(4) minutes. CS tear gas grenades fume for 1D4(2) minutes. Once their action is complete, smoke and gas lingers for about 15 more minutes in Calm conditions. Wind reduces this hang time dramatically -- check the Quick Reference Wind Displacement Table below for dispersal times. Keep in mind that this is the approximate time it takes for the cloud to move through an area approximately 980 feet (300m) in diameter.

Incidentally, windblown smoke and gas clouds change shape while moving. Light Air to Gentle Breeze force winds produce an ovoid (egg-shaped) cloud, with the small end centered on the grenade. Moderate Breeze to Strong Breeze force winds produces a teardrop-shaped area of effect. Moderate and Gale force winds create an elongated cone shape; Strong Gale force wind and higher produces a progressively narrower ribbon of smoke or gas.

Because of their lower muzzle velocity and larger projectile size as compared to most other projectile weapons, Offensive and Defensive grenade types (with the notable exception of the M576 Multipurpose buckshot grenade) are also subject to lateral displacement. Wind coming from the left or right quarters (relative to the grenadier) displaces a grenade downwind after it is fired. Generally speaking, for every 5 mph (8 kph) of wind speed, the grenade deviates 1 foot (0.3m) from its intended target. To quickly integrate wind speed effects on Offensive and Defensive 40mm grenades, simply use the Wind Force number as a negative modifier to "bullseye" a target. As most grenades have a large blast radius, this usually makes little difference to the intended target. There is an old saying in the military: "Close only counts with horseshoes and hand grenades."

Below are tables with the suggested values for integrating the effects of wind on the various grenade types.

Wind Speed Cloud Displacement Table

Wind SpeedPer HourPer Min.Per Sec.

1 mph5,280 ft88 ft@1.5 ft

1 kph1,000 m@17 m@0.3 m

Quick Reference Wind Displacement Table

ForceDescriptionEffects: Land/Seamphft/sec.km/hrm/sec.Disp. TimeCloud Shape

0CalmStill, calm air, smoke will rise vertically.Water is mirror-like.<1N/A<1N/A15 min.Sphere

1Light AirRising smoke drifts, wind vane is inactive.Small ripples appear on water surface.1-33'1-51 m15 min.Ovoid

2Light BreezeLeaves rustle, can feel wind on your face, wind vanes begin to move.Small wavelets develop, crests are glassy.4-78'6-113 m10 min.Ovoid

3Gentle BreezeLeaves and small twigs move, light weight flags extend.Large wavelets, crests start to break, some whitecaps.8-1215'12-195 m6 min.Ovoid

4Moderate BreezeSmall branches move, raises dust, leaves and paper.Small waves develop, becoming longer, whitecaps.13-1823'20-287 m4 ½ min.Teardrop

5Fresh BreezeSmall trees sway.White crested wavelets (whitecaps) form, some spray.19-2432'29-3810 m3 min.Teardrop

6Strong BreezeLarge tree branches move, telephone wires begin to "whistle", umbrellas are difficult to keep under control.Larger waves form, whitecaps prevalent, spray.25-3142'39-4913 m2 ½ min.Teardrop

7ModerateLarge trees sway, becoming difficult to walk.Larger waves develop, white foam from breaking waves begins to be blown.32-3853'50-6117 m106 sec.Cone

8GaleTwigs and small branches are broken from trees, walking is difficult.Moderately large waves with blown foam.39-4664'62-7420 m90 sec.Cone

9Strong GaleSlight damage occurs to buildings, shingles are blown off of roofs.High waves (6 meters), rolling seas, dense foam, blowing spray reduces visibility.47-5476'75-8825 m72 sec.Ribbon

10StormTrees are broken or uprooted, building damage is considerable. Large waves (6-9 meters), overhanging crests, sea becomes white with foam, heavy rolling, reduced visibility.55-6389'89-10229 m62 sec.Ribbon

11Violent StormExtensive, widespread damage.Large waves (9-14 meters), white foam, visibility further reduced.64-72102'103-11733 m54 sec.Ribbon

12HurricaneExtreme destruction, devastation.Large waves over 14 meters, air filled with foam, sea white with foam and driving spray, little visibility.73+116'118+38 m47 sec.Ribbon

Note: This table is based on the Beaufort Wind Scale used by the U.S. National Weather Service.