M249 Squad Automatic Weapon, 5.56mm,

NSN 1005-01-127-7510, LIN M09009
NSN 1005-01-451-6769, LIN M39263

The M249 Squad Automatic Weapon (SAW) provides a heavy volume of close and continuous fire needed to accomplish the mission, and they can engage targets beyond the capability of individual weapons with controlled and accurate fire. The SAW is the designation for a sub-family of the FN Minimi squad automatic weapon. The M249 is an air-cooled, gas-operated, fully-automatic-only firearm that fires from an open bolt position. It can accept belts of linked 5.56x45mm NATO (.223) ammunition through the top-mounted feed tray or M16-type magazines through the side-mounted port. The latter allows a SAW gunner to use riflemens' magazines in an emergency if he runs out of belted ammunition, though this often causes jams as the magazine spring cannot adequately keep up with the weapon's high rate of fire. Linked ammunition can be fed from either a loose belt or from a plastic box (or cloth pouch) for 200 rounds, clipped under the receiver. The hard plastic box has issues with being insecurely attached and by producing noise with movement in its standard form. The M249 SAW features a built-in bipod and a tripod-mounting lug for supported fire, as well as a quick change barrel that helps prevent overheating during sustained fire. Barrels are engaged and disengaged by rotating the built-in handle, and a spare is normally carried slung in an "A-bag" by the gunner or his assistant. The forearm is designed to contain a small cleaning kit for field use, though it may not be stored there in practice.

(Don't try this at home!)

For training exercises, the M249 is used with the M249 Blank Firing Adaptor (NSN 1005-21-912-8997), essentially a steel plug which screws into the muzzle and partially blocks it. (While standard blank firing adaptors for the M16 and M4 family of weapons will fit into the barrel of the M249 SAW, their use has been abandoned in favor of a SAW-specific BFA, due to the risk of catastrophic failure of the weaker rifle BFA, which is not durable enough for sustained automatic fire.) Gas-operated weapons rely on the projectile to trap gas pressure in the system as it leaves the barrel; without this, there will be insufficient pressure to cycle the weapon. U.S. M249s are sometimes fitted with the M145 MGO, a low-power optic that fits on via a top M1913 rail, when the rail is fitted. The regular M249 does not have a rail, however. The M249 mod kit increases the weight to 16.41 pounds.

United States military doctrine describes 3,600 m as the maximum range. Effective ranges include 800 m for a point target, 1000 m for an area target, and 600 m for suppression (suppression fire is attained by keeping the maximum height of the rounds no more than 1 m off the ground). Tracer ammunition burnout is at 900 m, however. The advised rates of fire are 85 rounds per minute with no barrel changes. With a barrel change every two minutes, this increases to 200 rounds per minute. For a barrel change every minute, the rate of fire can go up to 850 rounds per minute, which is approximately equal to the cyclic rate of fire, at about 850 to 900 round/min.

In addition to its traditional use as an infantry weapon, the M249 is also sometimes used as a vehicle-mounted weapon, most often on Humvees, either in the normal roof mounting (manually or remotely operated as part of a system such as the CROWS mount, sometimes in addition to heavier weapons such as an M2 Browning machine gun), or on a swing arm mounting accessible by the front passenger seat. It is also one of the weapons that can be mounted on the SWORDS robot.
(Content extracted from Wikipedia)

PS Magazine Articles

Dec 2007:  Do not use the M60 pintle to mount the M249....

Specifications:

SPECIFICATIONS	M249
Weight	15.07 lb (6.85 kg)
Length	1040 mm standard
Muzzle Velocity	965 m/s
Rate of Fire	Cyclic 650-850 rds/min
Effective Ranges: Point	600 m
Area	800 m

Variants:

M249E3	5.56x45mm NATO FN Minimi Para machine gun variant; shorter barrel
M249E4	5.56x45mm NATO FN Minimi SPW machine gun; also incorporating PIP kit improvements
Mk 46 Mod 0	5.56x45mm NATO FN Minimi SPW/M249E4 machine gun variant; fixed buttstock and improved rail handguard.
Mk 46 Mod 1	5.56x45mm NATO FN Minimi SPW/M249E4 machine gun variant; fixed buttstock, an improved rail handguard and has a 200 round box magazine. Currently in service with certain USSOCOM units.

M249 Para with Detached Standard Barrel and Buttstock

MK46 Model 0