The Americans finished World War II with a collection of machine-guns from the drawing board of John Browning. They were all of World War I origin, and American exposure to the weapons of their enemies and Allies had shown that there were other ways to make machine-guns; and some of them were more practical than the Browning for various applications.
One wartime innovation that attracted the Americans (and others) was the German concept of a general purpose machine-gun, a weapon that could be a squad automatic on a bipod, light enough to be carried by one man but robust enough to operate in sustained-fire weapon when fitted on a tripod.
The concept of the General Purpose Machine Gun in the United States was accelerated during World War 2 by confrontation with the German MG34 and MG42. The German MG42, it was felt, was the way to go.
In 1944 a captured MG42 was dissected and American designers set about adapting it to their concept of a machine-gun. When the result appeared it proved to be a failure due to a draughtsman's misreading of a vital dimension; by that time the war was over so the project was scrapped.
The Allies had been impressed with the flexibility provided by the German GPMGs, and the first US prototype GPMG was designed along the lines of the MG42 in a series of guns in the series T44, T52. When the early series proved disappointing, however, incorporating a modified belt feed mechanism based on that of the German MG42, with the gas operating mechanism of the German FG42 paratroopers' assault rifle provided significant improvements and the T161 series emerged and was pronounced ready to enter service as the M60 GPMG (see Technical Specifications).
The resulting machine-gun went into service in 1957 as the M60, chambered for the 7.62-mm NATO cartridge and acting as partner to the new 7.62-mm M14 rifle.
The prime producer of the M60 has been the Maremount Manufacturing Co of Saco in Maine, and large numbers have been produced to equip all arms of the US forces. Despite the protracted development of the M60 it still has some debatable features - the barrel heats quickly and is not easy to change rapidly, and the carrying handle is fragile and awkward. Also the M60 is rather on the heavy side for use as a squad weapon. Mounted on the M122 tripod, the M60 has limitations on sustained fire. Vehicle mounting is the M4 pedestal mount. Basically, the M60 is gas operated and can fire automatic only from a disintegrating metallic-link belt.. As the first round travels down the barrel, it pushes gas into the gas cylinder through a hole in the bore. The pressure generated in the cylinder then forces a piston down the chamber, moving the bolt back and bringing the next round into place. Once the firing pin hits the bullet and sends it speeding out of the barrel, the cycle is repeated for as long as the trigger is depressed.
With no gas regulator on the gun. however, there were drawbacks to this mechanism. Accumulated dirt or dust would slow the piston down and result in the M60 either jamming or 'running away'. The latter term refers to the weapon continuing to fire even when the finger is removed from the trigger. An extremely unnerving problem to deal with during the heat of battle, the assistant M60 gunner would have to hold on to the ammunition belt in order to stop it feeding.
A bipod is fitted as standard and is also used for barrel changing. As well as being the standard American GPMG, the M60 was also used by Australians.
The Australians introduced into the tactical use of the M60 two practices, based on experience in jungle, the first reaction firefight takes place with only a few rounds being fired off while the soldiers take cover. Australian gunners used to fit a short belt of only about 15 or 20 rounds on the gun, which was enough for the first firing. A full belt was fitted after going to ground. They also designed and manufactured a 'ready reaction magazine' of 28-40 rounds, enough for the initial exchange of fire, which fitted on to the belt carrier attachment of the M60 and fed into the ammunition feed tray. After taking cover, a full belt was loaded. The ready reaction magazine stuck out of the side of the gun 'a bit like on the old Sten Gun' as it was described by an Australian veteran of the Vietnam War.
The gun used in Vietnam had an odd arrangement of barrel, bipod and gas cylinder, which made barrel changing unnecessarily difficult and gave the gun's Number 2 crewmember an equally unnecessary weight to carry. The bipod and gas cylinder were permanently attached to the barrel, and the carrying handle fitted to the receiver. When firing on sustained fire, the exterior temperature of the barrel could reach 500ºF (literally glowing in the dark). To change the barrel, the whole assembly had to be removed, and this operation needed both crew members. Number 1 had to hold the gun secure by the butt and carrying handle, and Number 2 (wearing heat-resistant asbestos gloves) had to pull the barrel-bipod-gas cylinder assembly free after releasing the barrel locking lever. While Number 1 held the gun, Number 2 fitted the new barrel. Number 1 then had to readjust the zeroing setting to cater for the new barrel before resuming fire.
Experience gained led to the introduction of the M60El. The rather flimsy carrying handle of the M60 was replaced with a more robust one, and the gas cylinder and bipod mounted on the gun itself. The M60 had a straight-line recoil shape which made control easy when firing. It had the interesting features of a plastic heat guard on top of and underneath the body, forward of the trigger mechanism, and the bipod had heat shields attached so that when folded up the hands of the firer need not touch any hot metal. This was a great help when firing from the hip on the move or standing. A canvas belt carrier for a 1 00-round belt could be fitted to the left side of the gun, which kept the ammunition free of undergrowth. The gun weighed over 10kg (221b) and was 1,105mm (43.5in) long. it had a fixed blade foresight and a U-notch leaf rearsight. The M60's effective range was 1,000 m (1,094yd) on the bipod and 1,800m (1,969yd) on the M122 tripod.
The Australians introduced into the tactical use of the M60 two practices, based on experience in jungle, the first reaction firefight takes place with only a few rounds being fired off while the soldiers take cover. Australian gunners used to fit a short belt of only about 15 or20 rounds on the gun, which was enough for the first firing. A full belt was fitted after going to ground. They also designed and manufactured a 'ready reaction magazine' of 28 rounds, enough for the initial exchange of fire, which fitted on to the belt carrier attachment of the M60 and fed into the ammunition feed tray. After taking cover, a full belt was loaded. The ready reaction magazine stuck out of the side of the gun 'a bit like on the old Sten Gun' as it was described by an Australian veteran of the Vietnam War.
Some other changes also came along. The M60C was a modification that removed the stock and fitted a remote firing control, so that the gun could be slung on helicopters and fired by the pilot. The M60D had a spade grip fitted at the rear, for firing from helicopter doors. And the M60E2 was designed for use as a fixed tank coaxial gun, with a long exhaust tube and barrel extension to carry the propellant fumes out of the tank.
The M60 fires at about 550 rounds per minute, slow enough for a trained gunner to be able to loose off single shots or short bursts without the need for a special selector lever. It was also the first US machine-gun to have a quick-change barrel, but experience in combat showed that the designer hadn't quite got it right.
The barrel carried the front end of the gas cylinder and the bipod, so that when the gunner shouted "Change!" and released the locking lever, his assistant had to grasp the bipod and heave the barrel out of the gun while the gunner held it up in the air - or dropped it in the mud. The gunner had to keep holding it up while the assistant put the hot barrel to one side and inserted the new one, complete with its bipod; not the easiest of tasks on a dark night with a hot barrel, which is why a heavy asbestos glove was part of the assistant's kit.
As a sustained-fire gun on a tripod the M60 was fine; as a squad automatic, on a bipod, it was still somewhat heavy for its job, and eventually the Maremont Company developed what it called the 'Lightweight M60', which has now gone into service as the M60A1.