Ordnance Notes -- by Bob Stoner GMCM (SW) Ret.
M60 7.62mm Machine Guns (All Versions)
The current crop of rifle caliber machine guns after the Korean War were all John M. Browning designs: the M1917A1 heavy water-cooled; the M1919A4 medium air-cooled; and the M1919A6 light air-cooled. The Army wanted a new general purpose machine gun (GPMG) that was lighter than the lightest Browning (M1919A6); had a quick-change barrel (which the Browning did not); could be used as an infantry, vehicular, or aircraft gun; had an improved belt feed, and could be fired from either the shoulder, hip, bipod, or tripod.
Army Ordnance experimented with a T-series copy of the German MG42 general purpose machine gun in the mid-1940s. Ordnance even manufactured copies in .30 caliber. However, someone fouled-up the reverse engineering and made the receiver too short to accommodate the extra length of the American .30 caliber (7.62x63mm) cartridge vs. the German 7.92x57mm cartridge. The American replicas would not function and the project was abandoned at the end of 1945.
Ordnance did not give up and decided to incorporate features of several guns from its previous research. The new GPMG would use a modification of the American WW1 Lewis Gun gas and bolt system and the feed mechanism of the German WW2 MG42. The result was the M60 machine gun in 7.62mm NATO.
The M60 GPMG has several design features shared with the MG42: The M60 infantry gun has a butt stock and pistol grip/trigger group. The M60 has a combination hand guard and barrel shroud instead of the slotted barrel jacket of the MG42. The M60 has a folding bipod similar to the MG42 design and is adapted to a tripod mount.
The M60C was a helicopter machine gun. The butt stock and pistol grip of the M60 ground gun were removed. The butt stock was replaced by a sheet metal cover. The pistol grip was replaced by a solenoid-actuated trigger. The hand guard/barrel shroud was removed as was the bipod from the barrel. The M60C was mounted in two gun pairs on either side of UH-1 helicopters. The pairs of guns were slaved to the pilot's lead-computing sight. A mechanical buffer replaces the hydraulic buffer. The mechanical buffer raises the gun's cyclic rate of fire. The M60C is also used in pairs as part of the M-6 armament system on UH-1 helicopters (see below) and in the fuselage sponsons of OV-10 "Bronco" aircraft as used by Navy Light Attack Squadron FOUR [VA(L)-4] in Viet Nam.
The M60D was a flexible gun used by special operations units or helicopters. The butt stock was replaced by a pair of spade grips (similar to the .50 Browning MG). A trigger bar connected the triggers to the trigger group that replaced the pistol grip/trigger group of the M60. Barrels may or may not have bipods. Aircraft guns were fed through a flexible feed chute that attached to the side of the gun. The cradle of the aircraft gun incorporates a bag to catch expended links and brass as they ejected from the gun during firing. In Viet Nam, Mobile Support Team TWO users clipped a C-ration can to the bracket that was designed to hold the ammunition bandolier. The purpose of the C-ration can was to help the gun feed the ammunition more reliably.
The M60 is a general purpose machine gun that weighs 23 pounds, is air-cooled, gas operated, belt-fed, and fires full automatic. Length is approximately 43 inches. Cyclic rate is approximately 550 to 650 rounds per minute. Other versions of the basic M60 are the M60E1, M60E2, M60E3, and Mk 43 Mod 0 (aka M60E4).
The M60 has several quirks that caused users problems over the years. The barrel change lever could not be worked without asbestos gloves. Several important parts can be installed wrong which either render the gun inoperable or a single shot weapon. For instance, it was found that the mechanical buffer would stretch the gun's receiver if used for extended periods. The first attempt to cure the problems identified in the M60 was made by the M60E1.
The M60E1 was a redesign of the M60 to cure in-service problems of the various users. The new M60E1 revised the top cover to allow it to be closed when the gun was not cocked and the bolt was forward. The M60 could be damaged if someone attempted to close the cover on an uncocked gun. The M60E1 modified the bipod and moved it from the barrel to the gas cylinder. The carrying handle was removed from the M60 receiver and permanently attached to the barrel on the M60E1. The barrels of the M60 and M60E1 were not interchangeable; the M60 barrel incorporated the gas cylinder with the barrel and the M60E1 moved the gas cylinder to permanently attach it to the receiver. The forearm of the M60E1 was modified by removing the top to allow easier changing of a hot barrel. The gun was not put into production, but the design innovations it pioneered were incorporated into the M60E3 which was standardized.
The M60E2 is a co-axial machine gun mounted in armored vehicles, most notably the M1 Abrams tank. It has an extended barrel and gas cylinder to exhaust the gun gas outside the turret of the tank and keep it out of the interior. Like the M60C, the gun is fired by a solenoid. Unlike the M60C, the M60E2 has a manual trigger in case the solenoid fails. Weight is about 18 pounds.
The M60E3 is now standard with US Army, Navy, Air Force, and Coast Guard units. It has been replaced in the Marine Corps by the M240G and, with minor modifications, in the US Army by the M240B. (The M240 is a version of the Belgian MAG58 built by Fabrique Nationale of Herstal, Belgium, and has the boxy-receiver appearance of the old Browning .30 caliber M1919 series. The M240 is gas-operated and uses the same belted ammunition as the M60.) The M60E3 has a simplified butt stock, a modified and lightened forearm, a second pistol grip, a modified barrel with a permanently attached carrying handle and lightened, shorter flash suppressor. A lightened and modified bipod is attached to the gas cylinder as in the M60E1. Weight is about 19 pounds.
The Mk 43 Mod 0 is a modification of the basic M60E3 for Naval Special Warfare operators. Naval Sea Systems Command (NavSeaSysCom) at NAD Crane, Indiana, is responsible for the Mk 43 Mod 0. The Mk 43 retains the previous modifications of the M60E3 and the second pistol grip integrated into the forearm. The gas system is modified and a new lighter and shorter barrel is fitted. (The barrel is only slightly longer than the gas cylinder.) The flash suppressor has been modified to be more efficient with the shorter barrel. The Mk 43 retains the firepower of the M60 but eliminates over 5 pounds of weight. The reduced weight and length give the NSW operator more agility on the battlefield. Army special operations units call this gun the M60E4.
As this is written, NAD Crane has announced two new programs to replace the M60E3 and Mk 43 Mod 0 (M60E4) guns within the Naval Special Operations community. These guns are based on the Fabrique Nationale-designed M249 5.56mm squad automatic weapon used by the US Army and Marine Corps. The new weapons are designated Mk 46 Mod 0 for the 5.56mm SAW and Mk 48 Mod 0 for the 7.62mm SAW. The Mk 46 will use the belted ammunition of its M249 brother. The M48 will use the belted ammunition of the M60-series guns it replaces.
© 2005 Bob Stoner R5