M85 .50 Caliber Machine Gun
The recoil-operated M85 .50 caliber machine gun is designed for cupola mounting in armored vehicles. It can be fired electrically by the solenoid, or manually, at either high or low rates. One rate of fire is specifically for use against aircraft at 1000-1100 rounds per minute, with the other being for ground targets at 400-500 rounds per minute. It has a short receiver assembly, fixed headspace, and a quick-change barrel with flash suppressor.
The M85 machine gun has a capability of right- and left-hand feed. The left-hand feed is used on the M60, M60A1, and M60A3 tanks and M728 vehicles. The safety assembly and hand charger assembly are on the left. The right-hand feed is used with the safety assembly and hand charger assembly on the right.
Although the M2 .50 caliber machine gun was an excellent weapon, it was too large for many applications in armored vehicles and did not have a high enough rate of fire for effective use against aircraft. Following World War II, there was considerable experimentation with .50 caliber tank guns. The result was the development of the M85 .50 caliber tank machine gun. The M85 became the standard tank machine gun for a number of years.
Development of the T175 machine gun by Aircraft Armament, Inc. began in January 1952. The work, being done under contract to Springfield Armory, was on a short recoil weapon with a hydraulic accelerator to increase the weapon's rate of fire. The accelerator proved unreliable, especially in cold weather, and was replaced in November 1955 with a mechanical design. The new design was designated as the T175E1.
The work on the T175 series was as part of a broader development of alternative .50 caliber machine guns designs. This development also included the T42, T164, and T176 machine guns. The T42, being developed by the Ordnance Corps, was based on the .50 caliber M2 and M3 Browning machine guns. The T164, under development by Springfield Armory, was a revolver type weapon influenced by the German MG-213 automatic cannon. The T176, also designed by the Ordnance Corps, was a new design air cooled, recoil operated weapon. Issues with all of these weapons led to their terminations between 1955 and 1956, and subsequent focus on the development of the T175 series. The weapon was also under development concurrently with Springfield Armory's T197, a similar short recoil weapon, but in 7.62mm, which was eventually standardized as the M73.
The T175E1 was 10.9 inches shorter than the standard .50 caliber M2 machine gun and 20.9 pounds lighter. More importantly, it had a fixed head space, which allowed for a quick change barrel feature to be added to the weapon. Tests of the weapon did show, however, that the rate reducer that allowed for the high and low rates of fire was mechanically complex. This increased the weapon's cost and reduced reliability when the weapon was fired at the low rate of fire. The feeding mechanism was also not as robust as that of the M2 and jams could not be as readily cleared from the weapon. An overall reduction in durability, a product of the weight reductions, was also noted.
The feeding problems were in part a product of the original design of the disintegrating metallic links, which were found to be unreliable themselves. The links would get stuck in the feed mechanism and rounds would fall out of them due to the shock of firing, causing belts to break up. In 1959, a new design, based on the design of the link for the M60 machine gun, was introduced and designated as the XM15. The weapon was modified to accept these new links and was designated as the T175E2. In June 1959, both was type designated as standard, the XM15 becoming the M15, and the T175E2 becoming the M85.
The initial production of the weapon was conducted by Springfield Armory, with General Electric producing over 2,000 weapons between 1968 and 1970. In 1972, production of the M85 began at Rock Island Arsenal. Minor modifications and improvements to the design were conducted throughout most of its service. US Army Weapons Command conducted a survey in 1968 that showed over 20 percent of respondants appreciated the fixed headspace, quick change barrel, and variable rates of fire of the M85. 90 percent said the weapon was dependable. A variant adapted for infantry use was designated as the M85C, firing only in the low rate of fire and being equipped with spade grips. Reliability issues dogged the M85, however, and in the end it was supplanted by the weapon it had been expected to replace, the .50 caliber M2 machine gun.
The M85 .50 Caliber machine gun, which was unique to the M60 tank and the US Marine Corps LVTP7, proved to be operationally unreliable and ineffective against the existing generation infantry fighting vehicles when it was introduced (e.g., the Warsaw Pact BMP mechanized infantry combat vehicle). As of 1996, the US Marine Corps continued to store about 3 million .50 caliber cartridges loaded in belts using the M15 link designed for the M85 machine gun, even though the Marine Corps had removed the M85 gun from its inventory and no other weapon system uses this type of belt.
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