M252 81mm Medium Mortar

Gary's U.S. Infantry Weapons Reference Guide

The M252 81mm mortar is a smooth-bore, muzzle-loaded, high-angle-of-fire weapon. The components of the mortar consist of a cannon, mount, and baseplate.

The M252 medium mortar offers a compromise between the light and heavy mortars. Its range and explosive power is greater than the M224, yet it is still light enough to be man-packed over long distances. The M252 weighs about 93 pounds and can be broken down into several smaller loads for easier carrying. Rounds for this mortar weigh about 15 pounds each.

The M252 replaced the M29A1 in U.S. service.

The cannon assembly consists of the barrel that is sealed at the lower end with a removable breech plug, which houses a removable firing pin. At the muzzle end is a cone-shaped blast attenuator device (BAD) that is fitted to reduce noise. The BAD is removed only by qualified maintenance personnel.

The M177 mount consists of elevating and traversing mechanisms and a bipod.

• The bipod provides front support for the barrel and carries the gears necessary to lay the mortar. The barrel clamp, which consists of an upper and lower clamp, is situated at the top. The upper clamp is fitted with a locking arrangement that consists of a curved handle and a spring-loaded locking rod, which is ball-shaped at its lower end. The lower clamp is shaped and bored on each side to house the buffer cylinders. On its right side, the clamp is recessed to receive the ball end of the locking rod. A safety latch located at the side of the recess is used to secure the ball.
  
  
• The sight bracket is attached to the buffer carrier, which is fitted to the traversing screw assembly. Attached to the right of the screw is the traversing handwheel. The traversing screw assembly is fitted to the clamp assembly, which is pivoted in the center on an arm attached to the elevating leg. Attached to the arm is the cross-leveling mechanism, which is attached to the clamp assembly at its upper end.
  
  
• The elevating shaft is contained in the elevating leg; to the left of the elevating leg is the elevating handwheel. A plain leg is fitted to a stud on the elevating leg and is secured by a leg-locking handwheel. A spring-loaded locating catch is behind the elevating gear housing, which locates the plain leg in its supporting position for level ground. A securing strap is attached to the plain leg for securing the bipod in the folded position. Both legs are fitted with a disk-shaped foot with a spike beneath to prevent the mount from slipping.

The M3A1 baseplate is of one-piece construction, and supports and aligns the mortar for firing. During firing, the breech plug on the barrel is sealed and locked to the rotatable socket in the baseplate.

The sightunit is the device on which the gunner sets deflection and elevation to hit targets by using the elevation level vial and the cross-level vial. After the sight has been set for deflection and elevation, the mortar is elevated or depressed until the elevation bubble on the sight is level. The mortar is then traversed until a proper sight picture is seen (using the aiming posts as the aiming point) and cross-level bubble is level. The mortar is laid for deflection and elevation when all bubbles are level. After the ammunition has been prepared, it is ready to be fired.

The two major components are the elbow telescope and sight mount. The elbow telescope has an illuminated cross line. The sight mount has a dovetail, locking knobs, control knobs, scales, cranks, and locking latch.

The following are authorized (Standard B) cartridges for the M252 81mm mortar:

• High explosive: M821, M889, M374-series, and M362.
• Red phosphorus/white phosphorus: M819 and M375-series.
• Illuminating: M853 and M301-series.
• Training practice: M879, M880, M68, and sabot.

Click here for more information.

The mortar squad consists of five men. Their firing positions and principal duties are as follows:

1. The squad leader stands behind the mortar where he can command and control his squad. In addition to supervising the emplacement, laying, and firing of the mortar, he supervises all other squad activities.
   
   
2. The gunner stands to the left side of the mortar where he can manipulate the sight, elevating handwheel, and traversing handwheel. He places firing data on the sight and lays the mortar for deflection and elevation. He makes large deflection shifts by shifting the bipod assembly and keeps the bubbles level during firing.
   
   
3. The assistant gunner stands to the right of the mortar, facing the barrel and ready to load. In addition to loading, he swabs the bore after 10 rounds have been fired or after each fire mission. He may assist the gunner in shifting the mortar when the gunner is making large deflection changes.
   
   
4. The first ammunition bearer stands to the right rear of the mortar. He has the duty of preparing the ammunition and passing it to the assistant gunner. He is also the squad driver.
   
   
5. The second ammunition bearer stands to the right rear of the mortar behind the ammunition bearer. He maintains the ammunition for firing and provides local security for the mortar position. He performs other duties as the squad leader directs.