Science Fair Project Encyclopedia
M60 machine gun
|Caliber:||7.62 mm NATO|
|Firearm action:||Open Bolt, Gas-actuated|
|Barrel length:||22 in (560 mm)|
|Overall length:||42.4 in (1077 mm)|
|Effective range:||1202 yd (1100 m)|
|Maximum range:||4075 yd (3725 m)|
|Cyclic rate of fire:||~550 round/min|
|Sustained ROF:||100 round/min|
|Muzzle velocity:||2800 ft/s (853 m/s)|
|Weight, (unloaded):||23.1 lb (10.5 kg)|
The M60 machine gun (more properly known as the M60E1) is an American general-purpose machine gun, firing the 7.62 x 51 mm NATO cartridge. In the U.S. military, it has largely been replaced by the M240 machine gun.
The M60 can be used in both offensive and defensive configurations. In the offense, it provides a higher rate of fire, greater effective range, and uses a larger-caliber bullet than the standard U.S. assault rifle, the M16. In defensive use, the long-range, close defensive, and final protective fires delivered by the M60 form an integral part of a unit's battle plan.
The M60 is effective to 1,100 meters when firing at an area target and mounted on a tripod, to 800 meters when firing at an area target using the integral bipod, to 600 meters when firing at a point target, and to 200 meters when firing at a moving point target. U.S. Marine Corps doctrine holds that the M60 and other weapons in its class are capable of suppressive fire on area targets out to 1,500 meters if the gunner is sufficiently skilled.
The M60 is considered to be a "crew-served weapon" which means that it is usually operated by more than one soldier, in this case two - the gunner and an assistant. The gunner carries the weapon while the assistant carries a spare barrel and extra ammunition in linked belts. The basic ammunition load carried by the crew is 600 to 900 rounds, which at the maximum rate of fire allows for approximately two minutes of continuous firing. In many U.S. units that used the M60 as a squad automatic weapon in Vietnam, every soldier in the rifle squad would carry at least 200 linked rounds of ammunition for the M60, a spare barrel, or both, in addition to his own weapon and equipment.
The M60 machine gun began development in the late 1940s and borrowed strongly from German designs such as the MG42 and FG42, combining the stamped sheet metal construction and belt feed mechanism of the former with the often unreliable and exceedingly complex gas-actuated operating system of the latter. It was adopted by the US Army in 1957 and served for almost 35 years, not without substantial criticism by troops who used it in the field.
The gun first became widely known during the Vietnam War period and has appeared in numerous television shows and movies (perhaps the most well-known of these are the Rambo movies starring Sylvester Stallone). It was gradually replaced in the late 20th Century by the M240 machine gun (a license-copy of the FN MAG), which was finally adopted by the US military in 1991.
The M60 is a gas-actuated, air-cooled, belt-fed, automatic machine gun that fires from the open-bolt position. Ammunition is fed into the weapon from a 100 round bandoleer containing a disintegrating metallic split-link belt. As with all such weapons, it can be fired from the shoulder, hip, or underarm position. However, it is recommended that a bipod-steadied position or a tripod-mounted position be used as the weapon is heavy and difficult to aim when firing without support.
The original design of the M60 incorporated several features from the innovative German designs of World War II. The straight-line layout allowed the operating rod and buffer to run directly back into the buttstock and reduce the overall length of the weapon. The large grip also allowed the weapon to be conveniently carried at the hip. The gun can be stripped using a live round of ammunition as a tool.
When tested in the field, however, the M60 immediately displayed several severe problems. Some say that the most commonly complained of feature was weight, but all belt-fed weapons of this type are rather heavy.
From units in Vietnam, the single most common complaint was that the M60 was unreliable and prone to jamming and other malfunctions, especially when it was dirty (fine sand and dust in the mechanism tend to bring the M60 to an immediate halt). This was a major factor in the Israeli Defense Force declining to adopt the M60. The weapon was also more difficult to clean and maintain than the M1918 Browning Automatic Rifle, or BAR, that it replaced. The safety was awkward to operate and worked the "wrong way" for soldiers who were trained with the M16 rifle and M1911A1 pistol - that is, it required an upward movement of the thumb on the safety catch to make the gun ready to fire, rather than a downward movement as with the other weapons.
The M60 was also prone to tearing rims off of fired cartridge cases during the extraction cycle, resulting in failure to remove the empty case, causing a jam that could take many minutes to clear. The barrel latch mechanism (a swinging lever) had a tendency to catch on the gunner's equipment and accidentally unlatch, causing the barrel to fall out of the gun. The lever was replaced with a pushbutton mechanism that was less likely to be accidentally released, but many of the swinging-lever latches are still on guns in inventory, forty years after this problem was discovered. The grip/trigger housing assembly is held in place with a rather fragile leaf spring clip instead of the captive pins used in other designs. The spring clip has been known to be prone to breakage since the first trials at Aberdeen Proving Ground. Duct tape and cable ties are often seen on M60s in the field, placed there by their crews in case the spring clip breaks.
Several critical parts of early production M60s, such as the receiver cover and feed tray, were made from very thin sheet metal stampings and prone to bending or breaking; sturdier parts were eventually available in the early 1970s. Early M60s also had driving spring guides and operating rods that were too thin and gas pistons that were too narrow behind the piston head (part of an attempt to save weight), leading to problems with breakage. Metallurgical problems also played a part, (blamed by some on low-bid contractors), but after 1970 a slightly heavier part was designed and slowly put into the supply chain.
U.S. Marines especially despised the M60 and many Marine units held onto their BARs until 1967-68. The M60E3 variant was designed in the mid-1980s for the U.S. Marine Corps, with a reduction in weight to 18.9 lb (8.61 kg) and a slight improvement in reliability. However, users complained about the quickly-overheating barrel, which had been a problem with the original M60. After approximately 200 rounds had been fired within one minute, the hot barrel had to be replaced with a spare to prevent overheating. This occurred often during combat situations, and a crew member had to don heat-resistant asbestos mittens, further slowing down the process.
This problem was aggravated in the M60E3, as the lighter barrel required changing every 100 rounds instead of every 200. However, the M60E3's barrel has a wire and plastic handle near the breech end and can theoretically be changed safely without the use of mittens.
In 1991 the M60 was finally officially replaced with the Belgian-designed FN MAG machine gun, designated the M240 in U.S. service. However, many M60s remain in use with the U.S. Army Reserve and National Guard units. It is still a frequent source of complaints from the soldiery, despite the attempted improvements made since 1967.
The M60 family of weapons are capable of firing many different kinds of ammunition. Most common among them are the M61 Armor piercing, the M62 Tracer, the M80 Ball, the M63 Dummy, and the M82 Blank; the new tungsten cored M993 Armor piercing ammunition can be used with the M60 as well, though it did not enter the inventory until long after the M60 was withdrawn from service in active-duty units. When firing blanks, the M13 or M13A1 Blank Firing Adapter (BFA) is necessary in order to get the weapon to cycle full-auto with blanks. All of these ammunition types are delivered to the gun via a NATO standard disintegrating metallic split-link belt. The standard combat ammunition mix for the M60 consists of a four ball (M80) cartridges and one tracer (M62). The four to one ratio theoretically allows the gunner to accurately "walk" the fire into the enemy. A skilled machine gunner also knows that tracer bullets do not always fly quite the same trajectory as ball, and weapon's sights must be used—particularly at ranges in excess of 800 meters, where 7.62 x 51 mm tracer bullets usually burn out and are no longer visible (which is a problem with all weapons in this caliber; smaller-caliber tracer bullets, such as the 5.56 mm used in the M249 Automatic Rifle, hold even less tracer compound and differ greatly in weight from ordinary bullets. As a consequence, their trajectories are radically different from non-tracer bullets, and burn out at a mere 300 meters).
Many different variants of the M60 have been developed over the years. Most of the revisions have been aimed at rectifying problems with earlier designs; however, two versions (the M60C and the M60D) are modified for use in aircraft; the US Marine Corps also used the M60C as the coaxial gun in the USMC version of the M60A1 tank. In Vietnam, this last version proved to be so unreliable and so prone to jamming, parts breakage, and other problems that most Marine tank crewmen pulled out the M60C and replaced it with an old Browning .30 (7.62 mm) machine gun; in many Marine armor units in Vietnam that used the M60A1 tank, they also pulled out the gunner's rangefinding telescope, which was useless in close jungle combat, and replaced it with a second Browning .30 (7.62 mm) in a jury-rigged second coaxial mount. Some Marine tank veterans have remarked that they hated the M60C even more than they hated North Vietnamese troops with RPGs.
The M60s used by infantrymen had to be at least a little dirty before they would jam, but the M60D will jam even when it's perfectly clean, usually when the size of ammunition links exceed the C-model's very narrow range of specifications. It is not unheard-of for armorers with all their tools to take half an hour or longer to get the working again after a jam.
The first variation on the M60 was the M60E2. It was most commonly used as an external weapon on armored fighting vehicles.
The M60E3 was fielded circa 1986 in an attempt to remedy problems with earlier versions of the M60. It is a light-weight version intended to reduce the load carried by the gunner. Unlike its predecessor, the M60E3 has several updated modern features. It has a receiver-attached bipod (for improved stability), ambidextrous safety, universal sling attachments, a carrying handle on the barrel, and a simplified gas system. However, the aforementioned modern features also caused almost as many problems for the weapon as they fixed. The light weight barrel is not safe for sustained fire of 200 rounds per minute without catastrophic failure of the barrel. (Some personnel claim to have witnessed successful prolonged firing of the weapon. The stellite superalloy barrel liner that makes it possible, but the excessive heat generated by this process can quickly make the gun unusable). The reduced-weight components also reduced the durability of the weapon, making it more prone to rapid wear and parts breakage than the original. Most infantry units in the US Army and US Marine Corps have now switched over to the M240 as their general-purpose machine gun, which is far more reliable (particularly when dirty) and seems to be very well-liked by the troops for its ruggedness, despite the fact that it weighs five or six pounds more than the M60E3.
The M60C is an aircraft-mounted or coaxial version of the standard M60. The main difference between the standard M60 and the "C" designation is the electronic control system and the hydraulic swivel system used. It could be fired from the cockpit by the pilot or copilot. It was also the coaxial gun on M60A1 tanks produced for the US Marine Corps before 1975. It is an electronically controlled, hydraulic powered, air-cooled, gas-actuated, link-belt fed weapon. Before being replaced by the M240 system, it used the M2, M6, and M16 armament subsystems and was mounted on the OH-13 Sioux , the OH-23 Raven , and the UH-1B Huey.
The M60D is a vehicle-mounted version of the standard M60. It can be mounted on boats, vehicles and as a pintle-mounted door gun in helicopters. When used in aircraft, it differs from the M60C in that it is not controlled by the pilot, rather, it is mounted in a door and manned by a crewman. Like the rest of the M60 family, it is a air-cooled, gas-actuated, link-belt fed weapon. Unlike other models however, the M60D normally has spade grips and an aircraft ring-type sight or similar armored vehicle) and an improved ammunition feed system. A canvas bag is also affixed to the gun to control ejected casings and links, preventing them from being sucked into the rotor blades or into an engine intake. The M60D was equipped on the UH-1B Huey (using the M23, XM29, M59, and the Sagami mounts), the CH-47 Chinook (using the M24 and M41 mounts) in both door and ramp locations, the ACH-47A "Guns-A-Go-Go" variant of the Chinook (using the XM32 and XM33 mounts), and on the UH-60 Black Hawk (using the M144 mount).
- M2 Machine gun
- List of crew served weapons of the US Armed Forces
- List of individual weapons of the US Armed Forces
- List of firearms
- List of modern weapons
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