M252 mortar The M252 81 mm medium weight mortar is a British designed smooth bore , muzzle - loading , high - angle - of - fire weapon used for long - range indirect fire support to light infantry , air assault , and airborne units across the entire front of a battalion zone of influence . In the U . S . Army and U . S . Marine Corps , it is normally deployed in the mortar platoon of an infantry battalion . Design . The M252 system weighs 91 lb ( 41 kg ) completely assembled and is composed of the M253 Cannon ( 35 lb , 16 kg ) , M177 Mount ( 27 lb , 12 kg ) , M3A1 Baseplate ( 29 lb , 13 kg ) , and the M64A1 Sight Unit ( 2 . 5 lb , 1 . 1 kg ) . The mount consists of a base plate and a bipod , which is provided with screw type elevating and traversing mechanisms to elevate / traverse the mortar . The M64A1 sight unit ( also used on the M224 ) is attached to the bipod mount . The M252 is a gravity - fired smoothbore system . Attached to the muzzle of the weapon is the Blast Attenuation Device ( BAD ) , used to reduce the blast effects on the mortar crew . To increase cooling efficiency , the breech end is finned ; though first - hand accounts attest that the level of cooling is negligible . The cannon also has a crew - removable breech plug and firing pin . History . The M252 is an adaptation of the British 81mm L16A2 mortar developed in the 1950s . It entered service with the U . S . Army and replaced the previous 81 mm M29 mortar in 1987 . It was adopted due to the extended range ( from 4 , 500 meters to 5 , 650 meters ) and enhanced lethality . In the U . S . it is produced by Watervliet Arsenal . A much lighter version , the M252A1 , was fielded for the first time in 2011 . By reducing the number of parts and using lightweight materials , the total weight was reduced by 20 . 8 pounds . In the next several years , all U . S . Army M252s will be replaced by the M252A1 . As part of the same program , a lightweight version of the M224 mortar was developed . Operation . Crew . The M252 uses a crew of five enlisted personnel to operate : the squad leader , the gunner , the assistant gunner , the first ammunition bearer , and the second ammunition bearer . Types of rounds . While the M252 does fire a weapon specific series of ammunition , it can also fire rounds from the M29 Mortar ( only at charge 3 or below though ) . The M252 Mortar can fire the following principal classifications of training and service ammunition " Fuzes . The M224 rounds have two fuze types : the Multioption Fuze ( M734 ) and the Point - Detonating Fuze ( M935 ) . The M734 is used for the M720 HE round and can be set to function as proximity burst , near - surface burst , impact burst , or delay burst . Method of propulsion . The range of a mortar is controlled by what are referred to as " charges . " Charges are semi - circular nitrocellulose donuts that resemble a puffy letter " C . " Ammunition for the M252 mortar come with four charges . Longer range shots require more propellant than can be easily stored in the tail of the round , hence the necessity of the charges to be placed on the round . Once a target is ranged , the correct charge is placed on the round by removing the charges from the projectile . Once the charges are verified by the section leader , the round is dropped down the muzzle of the tube . The round , pulled by gravity , accelerates down the smooth bore of the mortar until the primer ( in the base of the tail boom of the round ) strikes the firing pin located in the bottom of the mortar tube . The primer detonates igniting the charge in the tail fin which in turn ignites any of the C - charges on the round . The expanding gas created by the burning charges push against the obturator band on the round , sealing the gasses and gives the round forward momentum . The round is accelerated by the gasses until it leaves the end of the tube .