M 14 and M60’s Gas Cut-Off System
M 60 Machine Gun
M 14 DMR
What is M 14?M
14 rifle, officially the United States Rifle, Chambered in 7.62 x 51mm NATO elder brother of 30-06 spring field. It became a standard issue NATO cartridge. It became the standard-issue rifle for the U.S Military in 1957, replacing the M1 Garand rifle in service with the U.S Army by 1958 and the U.S Marine corps by 1965; deliveries of service rifles to the U.S Army began in 1959. The M14 was used by the U.S Army, Navy, and Marine corps for Basic and Advanced individual Training from the mid-1960’s to the early 1970’s. M 14 is a Battle Rifle, it’s operating system is Gas operated rotating bolt, short stroke piston system. The mass of the rifle is 4.9 kg with loaded magazine, length is 44.3 inch and Barrel length is 22 inch with right hand 12:1 rifling with 4 grooves.
Rate of fire is around 700 to 750 rounds per minute, muzzle velocity is around 2800 feet per seconds, Effective firing range is 800m and maximum range is 3406m.
And the variants are M15 SAW, M14E1, M14E2/M14A1, M14M/M14NM, M14SMUD, M14EBR,M14 TACTICAL, M14 DMR, M39 ENHANCED MARKSMAN RIFLE, M 89SR MODEL 89 SNIPER, AWC G2A SNIPER RILFE, M21 AND M25 SNIPER RIFLE, GA SOCOM-16 M14 DMR.
What is M 60?
The M 60, officially the Machine Gun, Caliber 7.62mm, M60 is a family of American General Purpose Machine guns firing the 7.62x 51mm NATO cartridges from a disintegrating belt of M 13 links. There are several types of ammunition approved for use in the M 60, including ball, tracer, and armor piercing rounds. The mass of the M60 is 10.5kg, length is 43.5 inch and Barrel length is 22 inches.
When come into it’s action it uses Gas operated, short stroke gas piston, opened rotating bolt and the rate of fire fall around 550-650 rounds per minute. The muzzle velocity is 2800 feet per seconds, and the effective firing range is 1100m and the maximum firing range is 3724m. M 60 is a belt fed machine gun and it uses M 13 links. It was adopted in 1960 and issued to units beginning in 1960.It has served with every branch of the US military and still serves with the armed forces of other nations. It is manufactured and continued upgrade for military and commercial purchase continues into the 21st century, although it has been replaced or supplemented in most roles by other designs, most notably the M240 machine gun in U.S service.
The M 60 Machine gun began development in the late 1940s as a program for a new, lighter 7.62mm machine gun. It was partly derived from German guns of world war 2 (most notably the FG 42 and MG42) but it contained American innovations as well. The final evaluation version was designed the T 161 E3. It was intended to replace the M 1918 Browning Automatic Rifle and M 1919A6 Browning machine gun in the squad automatic weapon role, and in the medium machine gun role. One of the weapons tested against it during its procurement process was the FN MAG. The U.S army adopted the T 161 E3 as the M 60 in 1957. The decision to adopt the M 60 instead of foreign designs, like modified versions of the proven German MG 42 or the Still unproven FN MAG, was largely due to congressional requirements that preference be given to the designs of U.S arms manufactures primarily to avoid licensing fees, but also to support U.S firms.
The variants are T161, M60, M60E1, M60E2, M60B, M60C, M60D, M60E3, M60E4, M60E1, M60E2
What is Gas cut-off system in M 14 and M 60?
. Figure of M 14 Gas cut-off system
M 14 Piston
M14 Gas expansion chamber and gas block assembly
The gas cylinder design is essentially the same for the M 14 rifle and the M60 Machine gun, though dimensions are somewhat different.
The usual gas cylinder is operated by gas admitted when the bullet clears a gas port in the barrel. The gas at high pressure thus is admitted very suddenly, and its effect is that of blow on the piston. This is not the most desirable way to put mechanical parts into motion, though it is effective and in fact it is the system used in most current gas operated guns, generally quite successfully.
The gas system is another element that came off a World War Two experiment, this is actually on several of the E series experimental M1’s. And it is a gas system that was originally developed by and inventor named White. Basically it is called a gas expansion and cut off system.
The M14 and M60 gas cylinders are distinctive in being designed to deliver a prolonged push instead of a simple blow. This prolonged push is accomplished by admitting the gas into a chamber of considerable volume, where it is allowed to expand and push the piston back.
Function of the M14 gas cylinder is shown schematically in the illustration. Gas from the barrel enters the floating piston through a hole in line with the barrel gas port, and fills the space within the piston and the gas cylinder plug. The first movement of the piston takes the hole out of alignment with the gas port and automatically cuts off admission of gas and the gas port hole is no longer aligned with the piston hole. The considerable volume of trapped gas burn and expands smoothly and pushes the piston and operating rod to the rear. By the time the piston clears the exhaust port at bottom of the cylinder, the work of the gas has been done.
And the idea here is that it is a self-regulating system. So that if you have underpowered ammunition, the piston will take longer to start moving and more gas will come into the piston and it will operate properly. If you have over pressure ammunition, it will start moving faster and it will fill up faster, and it will cut itself off before too much gas gets in. And again you will have reliable operation, kind of regardless of the exact loading of the ammo, you can fire over pressure round without actually delivering extra energy to the gas system. And if you have an under pressure round this piston will start moving more slowly and it will open longer to allow it to again get the necessary amount of gas to fully cycle the gun. The main problem in M 60 is if you put the piston head in the direction of the muzzle, now you have nothing lined up with your gas port and you have a single shot machine gun.
In this construction the dwell time between firing and beginning of movement of the mechanism is about doubled. The velocity of the slide when it begins to unlock the bolt is only about half what it would be otherwise. Then the expanding gas continues to accelerate the parts, so that the over all time cycle is substantially the same as from the impulse of a plain gas cylinder. The low mechanical stresses and bearing pressures obtained with this comparatively slow and smooth acceleration are quite desirable, and contribute to the great endurance of the M 14 rifle.
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