The M60 (also seen as M-60) was intended to be a General Purpose Machine Gun (GPMG) that could perform all combat roles well enough. However, it proved to be heavy and unreliable in service, and was soon known as "The Pig" by American troops.
One of its primary disadvantages as a machinegun with a lightweight barrel, for field use rather than emplacement use, is that the barrel could not easily be changed for a fresh one, as the bipod and gas system were permanently attached to the barrel. This greatly limited the weapon's practical rate of fire, as the barrel should be replaced after roughly every 200 rounds when in rapid-fire engagements. Without being able to change barrels, gunners had to restrict their bursts of fully automatic fire to short, spaced ones rather than the longer bursts that machine guns are tactically intended for.
Further, its firing pin and other small parts of the firing system were notoriously weak and prone to breakage and failure.
The M60 was later revised to the M60E3 standard, lightening the barrel further, along with other components, and moving the bipod to the gas cylinder housing in order to allow quicker barrel changes. However, the lighter barrel meant that only 100 rounds could be fired between changes, rather than 200 as before, and a 200-300 round firing could destroy the barrel completely, rendering the gun useless. The additional lightening of other components also reduced the weapon's reliability in the field, though it did reduce the weight of the weapon.
The M60 series of weapons was largely replaced in service by the Fabrique Nationale (FN) Mitrailleuse d'Appui General (MAG), designed in Belgium and named the M240 in the U.S. military. Despite the fact that the M240 in its standard infantry configuration (M240B) is slightly heavier than the M60, it is vastly more reliable in the field and has a quick-change barrel, allowing sustained rapid fire. The M240 series also has a higher rate of fire (adjustable from approximately 650 rounds per minute to 950 rounds per minute), and uses the same 7.62mm NATO cartridge as the M60, the M24 and M40/M40A1/M40A3, and M21/M25 sniper rifles, the M14 battle rifle, and the M134 Minigun.