A riot gun refers to a type of firearm that is used to fire less than lethal ammunition for the purpose of suppressing riots. Riot guns may be special purpose firearms designed for riot control use, or standard firearms, usually shotguns and grenade launchers, adapted to riot control use with appropriate ammunition. Many of them are 37mm or 40mm caliber (about 1.5 inches).
Riot guns can fire various sorts of ammunition:
- Impact projectile. These rely on kinetic energy, e.g. rubber bullets.
- Teargas cartridge. This and the next are chemical riot control agents.
- Pepper spray
- Stun ammo
- Shotgun shell.
- Explosive. Largely for military use only.
- Incendiary. Largely for military use only.
- GLIMPS (Grenade-Launched Imaging Modular Projectile System). This is a 40mm caliber projectile which contains a small camera which transmits TV images of what it sees. See this link.
To avoid breaking the projectile up, riot gun cartridges are often propelled by black powder, which often when fired makes an eruption of sparks and smoke which is spectacularly large to those accustomed to modern cartridges propelled by more modern propellants: images   .
 Chemical agent ammunition
Chemical agents may be dispersed in two ways:
 Muzzle dispersion
This method is the simplest: the chemical agent is in the form of a loose powder, which is expelled by the propellant of the cartridge. These rounds are used at short range, and have effect from the muzzle to a range of about 30 meters (33 yards). This method is best used by operators wearing gas masks, as the chemical agent can easily be dispersed towards the operator, e.g. by the wind.
 Canister projectiles
These are also called gas grenades. They are used for longer range application. They are analogous to rifle grenades, providing increased accuracy and range over hand-thrown gas grenades. Gas grenades may be used by operators without gas masks, as the agent is only dispersed in the area of impact, as far away as 150 yards (137 m). The agent in gas grenades is dispersed as a gas or an aerosol spray.
 Ferret rounds
These are specialized gas grenades designed to penetrate light barriers, such as windows, hollow core doors, and interior walls, and disperse chemical agents on the far side.
 Impact rounds
Impact rounds come in a variety of shapes, sizes and compositions for varying roles. Impact rounds are made out of materials of much lower density than the lead normally used in bullets, and are fired at lower velocities. Some say that the low mass, moderate velocity, and large surface area prevent the rounds from penetrating the skin significantly, so they merely provide a painful blow to the target: but the public media have described instances where these impact rounds have caused surface injuries or have damaged eyes.
One broad classification of impact rounds is direct fire and indirect fire rounds. Direct fire rounds can be fired directly at the target, ideally targeted low on the target, away from vital organs that are more prone to damage from the impact. Indirect or skip fire rounds are intended to be fired into the ground in front of the target, where they dissipate some energy, and then rebound into the target.
 Baton rounds
Baton rounds are cylinders made of rubber, plastic, wood, or foam, and are the full bore diameter of the riot gun. Baton rounds may fire one long baton, or several shorter batons. Harder or denser baton rounds are intended for skip fire, while softer or less dense batons are intended for direct fire. Baton rounds are the subject of significant controversy, due to extensive use by British and Israeli forces, resulting in a number of deaths.
 Beanbag rounds
Beanbag rounds consist of a tough fabric bag filled with birdshot. The bag is flexible enough to flatten on impact, covering a large surface area, and they are used for direct fire. Beanbag rounds may be wide and flat, designed for close range use, or elliptical in shape, with a fabric tail to provide drag stabilization, for longer range use. (See also flexible baton round, a trademark for a type of beanbag round.)
 Rubber buckshot
These, also called stinger rounds, consist of a number of rubber balls ranging from around .32 inch (8 mm) to .60 inch (15 mm) in diameter, and are used for direct fire. The small diameter means that each ball contains far less energy than a baton round, but it also limits the range. Rubber slugs, used in 12 gauge firearms, consist of a fin stabilized full bore diameter rubber projectile. These are used for long range, accurate direct fire shots on individual targets.
 Pepper Ball rounds
Pepper-spray projectiles, commonly called pepperballs, are direct-fire paintball-like capsules filled with a pepper spray solution of capsaicin. They provide a longer range, more user-friendly way to disperse pepper spray. Many sorts can be fired from paintball markers. Other sorts are designed to be fired from specially-designed pepperball guns whose muzzle velocity is greater than a paintball marker: if the velocity is not high enough the projectile will not break. As a paintball impact is mildly painful, it can discourage rioters by itself, but the pepper spray incapacitates and discourages a larger number of rioters with each shot.
 Types of riot guns
Purpose built riot guns are commonly large bore guns, formerly 25 to 27 mm, modern versions are 37 to 40 mm. Dual purpose guns are usually 12 gauge (18.5 mm) riot shotguns, firing special less lethal shotgun shells.
Single-shot large bore riot guns, such as the Milkor Stopper 37/38 mm riot gun, M79 Grenade launcher and ARWEN ACE, are generally break open designs. The barrels are relatively short, resulting in a carbine sized gun, and may have a shoulder stock and/or a forward handgrip to provide greater control. Pistol riot guns do exist, but they are generally only used for short range, muzzle dispersing chemical agents.
Multishot large bore riot guns, such as ARWEN 37, are usually in the form of a revolver holding five or six rounds in the cylinder. Unlike normal revolvers, the cylinder of a revolving riot gun is too massive to be turned easily by the trigger pull, and is usually turned by a pre-tensioned spring or by a pump action.
Shotguns used for riot control are nearly always in 12 gauge, as that is the gauge in which nearly all riot control rounds are made. Generally riot shotguns are used, such as some models of the Remington 870 and Mossberg 500. Due to the reduced power of riot control rounds, there is insufficient energy to cycle the actions of gas operated and recoil operated firearms, so riot shotguns are manually operated, usually pump action. The advantage of using a riot shotgun for riot control is that the shotgun is a dual use firearm, and can switch quickly to and from the riot control role by changing the ammunition. The downside is that it can fire lethal projectiles, and so extra care must be taken in its use to prevent the wrong ammunition from being used.
A recent addition to the class of riot guns is the pepper ball gun, an example of which is the FN 303. This is essentially a paintball marker, either purpose built for riot control, or modified from a commercial paintball marker. The pepper ball guns use special pepper spray ammunition based on paintball technology, consisting of a gelatin capsule filled with the riot control agent. The guns use compressed gas and provide semiautomatic fire, and the pepperballs act just like paintballs, fracturing on impact and splattering the chemical agent on impact. These can be used for direct fire, to break the balls on the target, or indirect fire, breaking near the target and spraying the agent into the target's vicinity.
Police have been known to use paintball guns loaded with paint projectiles, to mark particular rioters so that police can easily identify and arrest them later.
Some weapons discharge teargas as a solution in water.
 Legal issues
Large bore riot guns are classified as firearms in the U.S., and are subject to BATFE regulations. Since firearms over .50 caliber (12.7 mm) with rifled barrels are considered destructive devices under the National Firearms Act, only smoothbore riot guns may be sold to civilians. 37 mm guns are smoothbore, and can be sold to civilians; a common form found on the civilian market are M203 grenade launcher replicas, which can be used to fire 37 mm practice rounds. 40 mm guns are usually rifled, and may fire 40 mm grenades; explosive grenades rely on the spin both for stabilization and for arming the fuze.
Riot shotguns are regulated in the same manner as other shotguns. Riot control ammunition may be restricted by different laws in various jurisdictions, to a lesser or greater degree than normal shotgun shells.
|ARWEN 37 & ARWEN ACE & variants||Police Ordnance|
|ARWEN 37||5||ARWEN 37: drum magazine, image|
|ARWEN 37S Riot Control Donut Launcher||37mm||5|||
|ARWEN ACE||1||ARWEN ACE, image on this page|
|CM-55 Gas Gun||37mm||1|||
|Cobray 37mm Launcher||37mm||1||, price $150–$200, aluminum barrel, retractable stock|
|Defense Technology 37mm Launcher||37mm||, single-shot & multishot versions|
|DPMS M-37 Flare Launcher||37mm||1||, price $200–$400|
|Federal Labs 37mm Rotary Gas Gun||37mm||6||, price $1700–$2000, rotary drum magazine, top-folding stock|
|FN 303||15||FN 303, drum magazine, fires small projectiles|
|H&K Launcher||37mm||1||, retractable stock|
|M203 grenade launcher||1||M203 grenade launcher, underslung attachment for rifle, image|
|M79 grenade launcher||1||M79 Grenade launcher, break-action, image|
|MGL-MK1 40mm Multi Launcher||40mm||6||, rotary drum magazine|
|Milkor Stopper||37/38 mm||1||Milkor Stopper 37/38 mm riot gun, break-action: image|
|MK40 40mm Under Barrel Launcher||40mm||1||, fits under rifle barrel|
|Ramo RT 37||37mm||1|||
|`Randy Shivak' M79 Grenade Launcher||40mm||1||, price range $1200 for the receiver|
|MK40 40mm Under Barrel Launcher||40mm||1||, 1-shot, fits under rifle barrel|
|Russian Single Shot Launcher RGM-40 "Kastet"||40mm||1||, 1-shot|
|SL1 Launcher||1||info & image|
|SL6 Launcher||37mm||6||rotary magazine, short info, info, image|
|TW73||1||TW73, breech load, image|
- And see http://37mm.com/launchers/
- This link (in German) describes a pistol-like weapon which can scatter 24 small pieces of CN gas or CS gas over 25 meters = about 80 feet square. It is called a Reizstoffwerfer = "irritant thrower", but that is a generic, not the name of the make.
- FM 3-22.31, 40-MM GRENADE LAUNCHER, M203 section 2-1.
- The SL1 & SL6 are made by Sage International Ltd & Sage Control Ordnance Inc