Grenade launcher A grenade launcher or grenade discharger is a weapon that launches a grenade with more accuracy , higher velocity , and to greater distances than a soldier could throw it by hand . Grenade launchers can either come in the form of standalone weapons ( either single - shot or repeating ) or attachments mounted under the barrel of a rifle . Some rifles have been designed to fire rifle grenade s , either from their muzzle or from a detachable muzzle - mounted launcher . Larger grenade launchers may be mounted on vehicles . Description . Most grenade launchers are man - portable , shoulder - fired weapons issued on a squad level , though larger launchers are sometimes mounted on armored vehicles . The most common grenade - round in use by modern militaries is the 40 mm fragmentation grenade , which is effective against a wide range of targets , including infantry and lightly armored vehicles . The ability of the grenade launcher to loft payloads in a high arc has resulted in many " specialty " grenades such as less - lethal sponge grenades , flares , and even a video camera that surveys the battlefield from a bird ' s - eye view . Heavier grenade launchers , such as automatic grenade launchers , are typically mounted on vehicles or in emplaced positions . These generally resemble a large machine - gun intended to rapidly launch grenades to suppress enemy activity in a target area . Muzzle - fired . Many grenades have been designed to launch from a rifle ' s muzzle , usually using either a special blank propellant cartridge , or more modern " bullet trap " and " shoot through " types which allow the grenade to be fired using live rounds . This system has two key advantages : the grenade can generally be made larger and more powerful as compared to underbarrel or standalone weapons , and the rifle ' s weight and handling characteristics are not affected as with underbarrel systems . The disadvantage of this method is that when a soldier wants to launch a grenade , he must mount the grenade to the muzzle prior to each shot . If he is surprised by a close - range threat while preparing to fire the grenade , he has to reverse the procedure before he can respond with rifle fire . Rifle grenades also tend to be more difficult to fire accurately compared to under - barrel or standalone designs . The SIMON breach grenade is a muzzle - fired grenade for breaching doors . The SIMON launches using a bullet trap to capture a standard 5 . 56 bullet fired from an M4 carbine or M16 . Shoulder - fired . The man - portable grenade launcher can come in the form of either a single - shot weapon or a repeating weapon resembling a large revolver or pump - action shotgun . Examples include the M79 ( single - shot ) and the Milkor MGL ( repeating ) . They fill the gap between the hand grenade and the mortar . Modern developments tend toward faster - firing grenades with a smaller blast radius to reduce collateral damage . The XM25 CDTE is a shoulder - fired , magazine - fed semi - automatic launcher firing 25 mm projectiles . It was originally a component of the XM29 Objective Individual Combat Weapon program , but modified to a larger caliber . A 12 Gauge grenade round called the Frag - 12 has also been developed for the Atchisson Assault Shotgun . Attached . Since grenade launchers require relatively low internal pressure and only a short barrel , a lightweight launcher can be mounted under the barrel of a traditional rifle . This reduces the weight the soldier must carry by eliminating the grenade launcher ' s buttstock and makes the grenade launcher available for use at a moment ' s notice . Underbarrel tubes generally have their own trigger group ; to fire , one simply changes grips , disengages the safety , and pulls the trigger . In Western systems , the barrel slides forward or pivots to the side to allow reloading . Soviet / Russian launchers are instead loaded from the muzzle , with the cartridge casing affixed to the projectile in the style of a mortar shell . For aiming , attached grenade launchers typically use a separate sight attached to the rifle ' s frame alongside the iron sights , or attach a flip - up sight directly to one of the rifle ' s sights . Examples of modern attached grenade launchers are the M203 , GP - 30 , AG36 , and FN40GL which mount to service rifle s . A late development is the 3GL from Metal Storm . As with most Metal Storm products , this weapon contains three electrically ignited grenades stacked front - to - back in a single tube to eliminate reloading . Automatic . Automatic launchers include the Mk 19 , AGS - 17 , and the HK GMG , which all fire at a higher velocity than related shoulder - fired grenades . They generally function as large - caliber machine guns with a relatively low rate of fire , used from an emplaced position in a similar way to a heavy machine gun . The heavy equivalent of the XM29 is the XM307 ACSW automatic grenade launcher that is easily convertible between the 25 mm grenade ammunition and standard . 50 BMG cartridges . Both are intended to fire programmable " smart " grenades capable of being set to explode at a certain distance from launch or at a certain height above the ground . This gives the ability to hit targets inside rooms or behind hard cover that would normally not be reachable by small arms fire .