In current usage, a riot gun or less-lethal launcher is a type of firearm used to fire "non-lethal" or "less-lethal" ammunition for the purpose of suppressing riots or apprehending suspects with minimal harm or risk.^[1] Less-lethal launchers may be special purpose firearms designed for riot control use, or standard firearms, usually shotguns and grenade launchers, adapted for riot control use with appropriate ammunition. The ammunition is most commonly found in 12 gauge (18.5 mm/.729 inch) shotguns and 37mm (1.46 inch) or 40 mm (1.57 inch) grenade launchers.

This article contains weasel words: vague phrasing that often accompanies biased or unverifiable information. (March 2009)

In the United States, the term riot gun more commonly refers to a riot shotgun.

Less-lethal launchers can fire various sorts of ammunition, including:

• Impact projectiles, which rely on kinetic energy, such as baton rounds, bean bag rounds, or rubber bullets
• Tear gas cartridge
• Pepper spray
• Stun rounds
• Smoke round
• Less-lethal shotgun shells
• Less-lethal grenades
• Sound-emitting projectiles
• GLIMPS (Grenade-Launched Imaging Modular Projectile System), a round containing a small camera that transmits images

To avoid breaking the projectile up, less-lethal cartridges are often propelled by gunpowder, which, when fired, may make an eruption of sparks and smoke larger than those made by modern cartridges propelled by smokeless powder.

Purpose-built launchers are commonly large bore guns, formerly 25 to 27 mm (0.98 to 1.06 inches), modern versions are 37 to 40 mm (1.46 to 1.57 inches). Dual-purpose guns are usually 12 gauge (18.5 mm/.729 inches) riot shotguns, firing special less-lethal shotgun shells.

Single-shot large bore launchers, such as the Milkor 37/38mm and 40mm Stopper, M79 grenade launcher, ARWEN ACE, and RGS-50M, 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 launchers exist, but are generally only used for short range, muzzle dispersing chemical agents.

Multishot large-bore launchers, such as the 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.

The pepper ball gun, an example of which is the FN 303, 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.

Large-bore launchers are classified as firearms in most countries. Shotguns intended for riot use are semi-automatic shotguns subject to relevant regulations. Riot control ammunition may be restricted in various jurisdictions, to a lesser or greater degree than normal shotgun shells.

Riot guns have been documented to be lethal in some cases, with the use of an FN 303 by the Boston Police Department in October 2004 resulting in the fatal shooting of Victoria Snelgrove being one such incident.^[6]