105-мм и 106-мм безоткатные орудия M27 и M40: развитие и применение.

A limited number of M50 Ontos were built as a self propelled light armored tracked anti tank vehicle. They had six 105 mm M40 recoilless rifles as its main armament, which could be fired in rapid succession against a single target to guarantee a kill. Replacing the M27 recoilless rifle, the M40 primarily saw action during the Vietnam War and was widely used during various conflicts thereafter in Africa or in the Middle East. It was replaced by the BGM 71 TOW anti tank missile system in the US Armed Forces.

The earlier M27 recoilless rifle was a 105 mm weapon developed in the early 1950s and fielded in the Korean War. Although a recoilless rifle of this caliber had been a concept since the Second World War, the weapon was hurriedly produced with the onset of the Korean War. The speed with which it was developed and fielded resulted in problems with reliability caused by trunnions that were mounted too far to the rear. The M27 was also considered too heavy by the U. S. Army and had a disappointing effective range due to the lack of a spotting rifle. Taking the M27 as the basis for a new design, the Army developed an improved version of the M27 that was type designated the M40 106 mm recoilless rifle in 1955. Although unsuitable for military purposes, M27 recoilless rifles were used to trigger controlled avalanches at ski resorts and mountain passes in the United States.

The M40 is shaped like a long tube with an M8C .50 cal spotting rifle above. The spotting rifle fires a round whose trajectory closely matches that of the 105 mm round and gives off a puff of smoke on impact with the target. On the left side, there is an elevating wheel, in the center of which is the trigger wheel used to fine adjust the elevation and at the same time firing the spotting rifle when pulled, and the gun when pushed. The mounting is a tripod, but the front leg has a castering wheel. On top of the mount is a traverse wheel. On the center of the traverse wheel is a locking wheel, when the wheel is down, the rifle is locked in traverse, and can only be moved right and left with the traverse wheel. When the wheel is raised, the rifle can be traversed by hand. Austria produced a two wheeled mount for the M40. The whole mounting can be placed on an M151 Jeep for mobile use. Hotchkiss M201 jeeps, Toyota Land Cruisers, Jeep CJs, Willys M38s, HMMWVs, M274 Mechanical Mules, Tiuna 106mm weapons platforms, JODDB (formerly King Abdullah II Design and Development Bureau) Al Jawad vehicles, RBY MK 1s, AIL Abirs and AIL Storms.

The ammunition for the M8C spotting rifle is not .50 BMG, but a 22m shorter (12.7x77mm) round than used in .50 caliber machine guns. The spotter round was developed to replicate the trajectory of the 106 mm ammunition, and features a tracer element and a point detonating incendiary filler to create a puff of white smoke at the impact point. Four of the six 106mm rifles on the M50 Ontos mounted spotter rifles. Spotter rounds has a yellow tip with a red band and practice cartridges had a green tip. Although the spotting rifle could conceivably be used in an antipersonnel role, historic U. S. military doctrine strongly discouraged this use, for a purely tactical reason—to conceal the vulnerable M40 and its crew from the enemy until the main rifle was ready to fire. However, this restriction is believed to be the source of a long standing misconception that the laws of war restrict the use of .50 caliber projectiles against enemy personnel more generally.

In the early 1990s, the United States Forest Service (USFS) introduced the M40 for avalanche control as ammunition stocks for its M27 rifles became depleted. The M40 was initially successful due to operational similarities to the familiar M27 and ready availability from the U. S. military; however, in 1995, a USFS gunner was killed by shrapnel after a low level premature warhead detonation inside an M40 barrel. The accident was attributed to an undiscovered hairline crack in the projectile's base plate. Following this incident, most USFS M40s were quickly replaced with surplus 105 mm howitzers, but a few were kept in service with safety barriers to protect the gunners, who fired the guns remotely. In December 2002, two M40s at Mammoth Mountain were destroyed by catastrophic bore explosions 13 days apart. The gunners were uninjured, having been protected by the safety barriers, but the incidents prompted the USFS to retire all remaining M40s in July 2003. Also in the mid 1990s, Parks Canada acquired four M40s for avalanche control to replace the Canadian Armed Forces using 105 mm towed howitzers in Rogers Pass (British Columbia) on the Trans Canada Highway. Special pedestals were built at specific locations and a pneumatic remote firing system was devised to allow the operators to fire the recoilless rifle safely in case of ammunition malfunction. After a trial period, the M40s plan was abandoned and the Canadian Armed Forces once again began providing 105mm towed howitzers and artillery personnel to conduct avalanche control.