Now See the Saw

by Peter G. Kokalis

On 1 February 1982 the M249 machine gun was officially adopted (type classified) by the United States Army. That America now has the finest, most reliable weapon ever placed into its small-arms inventory is due in large measure to a group of dedicated and impressively professional small-arms technologists at the U.S. Army Armament Research and Development Command (ARRADCOM) in Dover, N.J., and Aberdeen Proving Grounds, Md. Although not as startling or dramatic to either the media or public as the space-shuttle program, this major achievement will have far more important immediate consequences for our troops in the field.

The M249 5.56mm SAW (Squad Automatic Weapon) will be primarily deployed in the infantry fire teams of the U.S. Army and Marine Corps. It will replace the bipod-mounted M16A1 AR (automatic rifle) at the squad level and selected M60 GPMGs (general-purpose machine guns) in non-infantry units. The two fire teams in the rifle squad will each be issued an M249.

There has been an urgent need for a truly efficient squad automatic weapon. The obsolete Browning Automatic Rifle (BAR) should have been phased out In the mid-1930s. The BAR's deficiencies were many. It lacked a quick-change barrel (finally corrected in the post-war Belgian version), had a magazine capacity of only 20 rounds, positioned the magazine well In an awkward location which slowed magazine changes, all too frequently broke extractors, possessed a gas system which fouled far too readily, was clumsy to adjust and clean, was a poor performer in cold environments and weighed 19.4 pounds empty.

The M14A1 rifle with its bipod, front hand grip, pistol-grip stock and muzzle stabilizer was supposed to replace the BAR in the squad-automatic role. Chambered for the 7.62mm NATO round and weighing only 13 pounds loaded, the M14A1 proved incapable of accurate full-automatic fire. It illustrates the dilemma of those who insist on the use of .30-caliber cartridges in light squad weapons. If you want full-automatic capability with .30-caliber cartridges, the laws of physics will dictate a user-objectionable weapon weight.

Use of the bipod-mounted M16A1 proved unsatisfactory in the sustained-fire role. Experiments were also conducted in the employment of the M60 GPMG at squad level. As eventually evolved, the M60 is a totally successful medium machine gun. However, at 23 pounds unloaded, its debilitating effect on squad-level maneuverability was unacceptable.

During the period of 1972-74, the Squad Automatic Weapon (SAW) Project directed its attention to the muddy waters of caliber experimentation. The best known cartridge to emerge from this work was the 6x45mm XM732 steel-cased round which utilized a 106-grain projectile and had a muzzle velocity of 2,500 fps.

By October 1976, the 5.56mm SAW program was initiated with a Material Need Document (MND), which was later revised into a Joint Service Operational Requirement (JSOR), endorsed by the Army, Marine Corps, Air Force and Coast Guard. This JSOR described the need for a one-man portable, lightweight machine gun capable of providing effective suppressive fire out to a range of 1,000 meters and defeating all anticipated types of body armor. The M249 machine gun was selected from a competitive evaluation of four candidate systems.

The XM106 was developed by the Ballistics Research Laboratory at Aberdeen, Md. It is essentially a modified M16 firing from the open bolt, with a heavy, quick-change barrel, improved sight radius, using standard 30-round magazines or a riveted, spaced assembly of three magazines.

The XM248 was the second system. It was initially developed by the Rodman Labs at Rock Island Arsenal as a 6mm weapon, and then turned over to Ford Aerospace Communications Corp. for further design improvement and conversion to caliber 5.56mm. This unusual entry is belt-fed with rotary drive and operates by means of a unique dual gas system with a three-lug rotating bolt.

The third system was the SM262 produced by Heckler and Koch. The XM262 makes use of the usual H&K roller-locked, retarded blowback action. The belt system is sprocket-driven. It has a quick-change barrel and can be fired in either the semi or full-automatic modes.

The new 5.56mm XM249 SAW was developed by Fabrique Nationale of Belgium and first unveiled in 1974. Known in Europe as the FN Minimi, its development took place well before the NATO 5.56mm Second Caliber Standardization Agreement (STANAG 4172) to assure commonality of ammunition. It was a calculated risk that has paid off handsomely for FN and once again thrusts the company into the forefront of military small-arms technology.

Included in the type classification action of 1 February 1982 were the important new ammunition components of the SAW system. The M855 5.56mm ball cartridge uses the Belgian SS109 bullet which weighs 62 grains and contains a hardened-steel penetrator frontal core and lead base encased in a copper jacket. The bullet is green-tipped as this is the new NATO color code for this type of ammunition. This improved projectile requires a rifling twist of 1 turn in 7 inches to stabilize the bullet in flight, as opposed to the old M193 bullet which needs a twist of 1 turn in 12 inches.

The new M856 5.56mm tracer cartridge uses the new longer L110 projectile which weighs 64 grains and encases the tracer element as well as the lead core in a gilded metal-clad steel jacket, allowing for an unprecedented 900-meter burn-out. This was a much criticized area in the past.

The M27 link, like its Stoner predecessor, is a scaled-down M13 link (used with the M60 and FN MAG). The experimental XM27 links were first made by Borg Warner and later by Wells Marine Inc. I have been informed that a quantity of them were sent to the Navy SEALs for use with their Stoner 63 machine guns and that they did not work well (probably due to the Navy's almost worn-out Stoners rather than the new links).

For at least the first year FN will be supplying the ammunition which will be packaged and linked in a 200-round plastic assault pack with a ratio of four ball to one tracer.

The testing which resulted in selection of the M249 was an extensive and awesome process. A detailed examination of the SAW trials underlines the user-oriented nature of the test procedures.

The SAW trials commenced with a visual, non-destructive examination of all four candidate systems. Measurements were taken and parts-interchangeability tests were conducted. All four candidate weapons went through the entire test program. The guns were cleaned every 2,000 rounds. Cook-off tests followed and the rate of fire was specified at 85 rounds per minute without spontaneous detonation of ammunition in the chamber. While three of the weapons fire from the open-bolt position, the possibility of the bolt going into battery with a broken firing pin is conceivable. The machine guns were fired with and without lubricant and also tested for noise level. The position disclosure test examined the flash and smoke characteristics and the ejection power of each system.

The weapons were then immersed in salt water for a period of time, while loaded, and fired without cleaning. The guns were also placed in a temperature humidity cabinet for 10 days - to simulate a tropical environment - and again fired without cleaning. The mud tests were of two types. First the guns were dunked in the mud bath, quickly wiped off and fired. Then the weapons were dunked again and allowed to dry for four hours. After the mud was hurriedly chipped off, the guns were fired. In both instances only the muzzles were taped.

Two kinds of sand and dust tests were conducted. In the static test the weapons were laid in the material and then fired. The guns were fired with magazine and belt changes while the test medium was blown on them during the dynamic sand and dust test.

As rain washes away lubricants, a water spray test was held, followed by an icing test. The guns were also fired at extreme temperatures: 155°F and -50°F. The sustained-firing test involved firing 700 rounds in five minutes at varying rates of fire: 200 rpm for two minutes and 100 rpm for three minutes.

A ballistic performance test tracked the projectiles by radar. The trajectory of the new SS109 bullet is approximately the same as that of the M80 (7.62mm NATO) ball projectile. The accuracy and dispersion tests demonstrated that the considerable performance gap in crosswind effect between the 7.62mm M80 bullet and the old 5.56mm M193 projectile has been markedly narrowed by the new SS109 bullet. Results of the penetration tests were outstanding. The SS109 5.56mm bullet easily outperforms the M80 7.62mm, as it will penetrate the U.S. Army steel helmet at 1,100 meters.

The endurance test examined reliability and durability. Reliability is a user measurement of the mean rounds between failures. There are three categories of failures: Class 1, Immediately Clearable, i.e., the gunner can clear the stoppage in 10 seconds or less by a simple action, such as re-charging the weapon; Class 2, Clearable, the stoppage will take longer than 10 seconds but less than 10 minutes to clear by the operator and may involve some disassembly and use of the cleaning-kit tools; and Class 3, Severe, a stoppage the operator cannot clear by himself, such as broken parts, and which requires an armorer. The candidate weapons were judged against minimum acceptable level of reliability and the so-called "Blue Sky," or hoped-for Specified Levels. With a 95-percent confidence factor that the next specimen would perform at the same plateau as the test gun, the XM249 exceeded the Specified Reliability Levels in Class 1 and 2 failures and came close to the Specified Levels in Class 3 failures. A 50,000-round receiver life is expected. The Minimi's overall performance was outstanding and it was the clear winner of the SAW trials.

A subsequent extensive Operational Test (OT1) of the XM249 was held at Ft. Benning, Ga. The results reinforced the SAW trial conclusions. The XM249's performance was so superlative that the Army decided there was no need for the normal follow-on OT2. The only remaining critical OT issue was the hit capability of the XM249. To address this, the Marines, using a platoon of their own operators, conducted exhaustive hit-probability experiments at Aberdeen Proving Grounds, Md. The results far exceeded their expectations and, in general, the Army and USMC acceptance of their new squad automatic has been enthusiastic.

The M249 is gas-operated. When combined with a regulator, only gas operation can effectively control the available power to the specific needs of the moment. The M249's rotary gas regulator is a simplification of the FN MAG's regulator. It has two positions, normal and adverse, and is hand-adjustable. The adverse position increases the cyclic rate somewhat and it can be expected that fire-team leaders will all too often opt for this alternative. If this is done, however, it can be expected that reliability will deteriorate due to the increased cyclic rate. The only real disadvantage to gas systems is an increase in fouling over recoil-operated weapons - a problem compounded by the current emphasis on the use of ball-type powders. Ball propellants also generate more muzzle flash; however, they usually burn cooler than IMR-type powders, an acceptable trade-off, except when attempting to ignite tracer elements.

In normal operation, the M249's piston is forced to the rear by gas tapped from the barrel's ports near the muzzle end. The bolt carrier begins its rearward motion with the bolt itself still locked into the barrel extension. The chamber pressure has dropped to an acceptable level by the time a cam in the bolt carrier rotates and unlocks the bolt. Gas escaping from the system is directed upward into the atmosphere, not downward as with the M60, which is notorious for its position-disclosing dust swirls.

Extraction problems have plagued 5.56mm weapons. The M249's remarkable reliability is largely a consequence of an extraction process which is initiated only after its rotary bolt has unlocked. This delay allows the case to contract and release its frictional grip on the chamber walls. The two rails welded to the receiver walls on which the bolt and carrier ride throughout the extent of their travel also contribute significantly to the smoothness of operation and the unique absence of stoppages and parts breakage.

Rotary bolts have been in use for some time. Early examples include the little-known Czech ZK 420S rifle in 7.92mm and the Johnson M1941 and M1944 light machine guns. The M60 GPMG, the M16 and the famed Kalashnikov assault rifles also utilize rotary bolts. In most of these systems the bolt is locked into lugs in the barrel extension rather than the receiver, as is the case with the M249: It results in more positive head space and allows cheaper, lighter construction of the receiver. The M249's steel receiver utilizes welded joints rather than pins and riveted construction.

Innovative features abound on the M249, not the least of which is its amazing capacity to accept either disintegrating link belts or the M16 30-round box magazine without modification. It is intended that riflemen in the squad will turn over magazines to the M249 gunner only in an emergency. When a belt is in the feed tray it covers the magazine port. Likewise, an inserted magazine protrudes outward to warn against simultaneous insertion of a belt. Under normal circumstances the M249 gunner will move out with 600 rounds of ammunition, 200 in the assault pack attached to the weapon and two additional 200-round assault packs attached to his web gear.

Two hundred rounds of linked 5.56mm weigh about six pounds as against 12 pounds for 200 rounds of linked 7.62mm. That's an 18-pound difference in a 600-round load, plus an additional seven-pound saving in weapon weight over the M60. Although this may be scoffingly dismissed by gun writers who continue to advocate .30-caliber weapons, anyone who has humped the boonies will breathe a sigh of relief.

The M249 has a chrome-lined bore and a three-second quick-change barrel. Unlike the M60, the M249's feed cover can be closed with the bolt in any position along the feed cam. The tubular-aluminum skeleton stock and its folding wire buttstrap are weight-saving contributions to the gun's comfortable 15.5 pounds. The M249's push-button safety and elimination of the semiautomatic mode simplify the sear mechanism. A loaded belt indicator has been provided for night use and the rear sight is adjustable to 1,000 meters.

At present the M249 uses the standard FN FAL pistol grip, but this will be altered in the production models. The grip angle will not be as sharp, the bottom flare will be eliminated, a finger swell will be incorporated below the trigger guard and the current U.S. lubricant bottle will be inserted.

The M249 can be fired from the M122 tripod, using the M60 pintle and a different adaptor for the T&E (Traverse & Elevation) mechanism. The M122 tripod is of course the old Browning M1919A4/A6 M2 tripod modified for use with the M60 after the mount originally Intended for the M60 (the M91) self-destructed during the Aberdeen tests. While not entirely satisfactory. the M122 tripod is already in the inventory and, in any event, the M249 is expected to see little use in this configuration. The M249 can also be mounted on the FN MAG tripod, a far sturdier affair.

The Marines expect to issue each M249 gunner with one spare barrel. At this time the Army has no plans to issue spare barrels at the squad level.

During the tests which led to its adoption, 29 different XM249s had more than 500,000 rounds fired through them. Unlike most gun writers, who can tell you everything you will ever need to know about a particular weapon after firing less than 100 rounds through it, it would be more than presumptuous of me to imply that observing and firing 500 to 1,000 rounds through the M249 in one afternoon could possibly generate any really significant conclusions. The weapon I fired had already more than 10,000 rounds fired through it. The only time this vicious little jewel stopped cranking was during belt changes. I encountered no malfunctions or stoppages of any kind.

I fired the M249 from the prone, kneeling and standing positions and from the hip assault position, using the M60 padded sling (which will be issued with the gun). Its handling characteristics border on the phenomenal. While less than 22 pounds with a loaded 200-round assault pack, the standing position is nevertheless an expediency measure only. The weapon is far more comfortable to fire for more extended periods of time in the kneeling and hip assault positions. When down in the prone position, watch out! It's deadly. The hit capability is literally astounding. With a cyclic rate of 750 to 950 rpm (dependent upon ammunition, gas regulator setting and degree of fouling present), it was difficult for me to tick off bursts of less than three to four rounds. However, the hit probability is so high that the Army actually recommends five- to six-round bursts.

Although I have fired more than several hundred different types of automatic weapons, I have never been more impressed. The M249 is quite obviously the right choice at the right time by a pretty damn righteous group of people. The M249 should be in the hands of the troops some time between December 1983 and March 1984. Thank God.

first published in the August 1982 edition of Soldier of Fortune Magazine