The History and Development of U.S. .50 Caliber Ammunition

By Barry Sturk

Anytime you have the pleasure of attending one of the Knob Creek or Hiram Maxim machine-gun shoots, you can always count on seeing the crowd ardently anticipating the guy with the Browning fifty caliber squeezing the trigger on a nice long belt of ammunition. You can say what you want about that beautiful Argentine Maxim machine-gun that looks more like a work of art than a gun, but when that .50 caliber sounds off with a crescendo of almost heart stopping force, all eyes are trained to one place, on the fifty cal.

Throughout the history and development of small arms there has probably not been a more prolific development then the Fifty caliber. The capabilities of this round make it one of the most versatile and important calibers in combat today. The fifty caliber’s ability to be deployed by one individual and give that person the capability of discretely engaging a target at ranges of over one mile away are definitely alluring from a tactical standpoint. While the .50 cal sometimes seems to be exaggerated, it is hard to imagine a round that at ranges of over a mile and a half away, has more kinetic energy than a .44 Magnum, and has unbeatable penetration as well.

After WW I the United States Military expressed the need for a larger caliber round that was at least one half inch in diameter and had a muzzle velocity of 2,700 fps. Due largely to the fact that by the end of WW I the Germans had started deploying much heavier armored aircraft and conventional caliber ammunition had little or no effect on them. After careful consultation in 1918 with the American Expeditionary Forces and the Army Ordnance Department, it was decided that .50 cal would have its primary use intended for aircraft machine-guns. At the onset, the American .50 caliber was greatly influenced by the German 13mm tank round, the “Tank und Flieger” and at the same time the Ordnance Department was also conducting tests on the French 11mm round in a Browning firearm as a possible alternative, but the 11mm round proved ineffective.

The first machine gun that the U.S. used the fifty caliber round in was the Browning Model 1918 on October 15, 1918 at which time 900 rounds of the new .50 cal were shot though an equally new Browning firearm. During the very first tests conducted on the new .50 caliber both rimless and rimmed rounds were used with various case lengths. The world had just gotten a glimpse of what would prove to be one of the most important weapons of the century.

The .50 caliber ammunition was manufactured by Winchester from 1918-1919 after which Frankfort Arsenal took over. Frankfort did some minor changes to the round such as increasing the chamber pressure to 52,000 psi and increasing the muzzle velocity. The model 1918, which had a cyclic rate of 500 rpm, shot the new .50 cal bullet that was 5.25 inches long and had a 707grain bullet and a velocity of 2,300. Although the Model 1918 was never officially adopted by the military its successor, the Model 1921 Browning .50 cal was finely adopted by the military in 1925, although the first fifty caliber round that was adopted was earlier in 1923. The case was a gilding metal jacket with a bullet comprised of a steel core in a lead sleeve which had a weight of 51.3 grains. The first round that had an official designation though was the M1 boat-tailed .50 in 1931. But still the military had higher expectations for its fifty caliber round. Basically any improvements to the .50 caliber round were unremarkable until 1937, due mostly in part to the lack of funding for the project because of the Great Depression. In 1937 though the fifty-caliber ammunition underwent various propellant improvements which resulted in the velocities up to 2,700fps. Further testing in the 1940’s by reducing the projectile weight from 750 grain to 710 grain increased the velocity to an incredible 2,810,with a chamber pressure of 55,000 psi and it was capable of penetrating an astonishing 3/4 of an inch of armor plate at 600 yards. The M1 round was now replaced in 1941 with the newer M2 version.

The fifty caliber was now an incredible new force to be reckoned with in the U.S military arsenal. In the early 1940’s it was recorded that well over 1million Browning Machine Guns were produced for the U.S military. Every one from A C Spark Plug to General Motors and Frigidaire was now manufacturing the Browning Machine Guns for the military, and during the war ammunition companies worked 24 hours a day producing the .50 caliber rounds.

Since the adoption of the fifty caliber by the military it has probably been one of the most experimented, and used rounds, in the military arsenal. Ammunition is produced in over 30 countries and has more than 100 different variations. While being produced by many other countries its composites remain mostly the same. The cartridge case is rimless, bottle-necked, mainly made of brass, the propellant is single or double base, and the jacket is Gilding metal. The cartridge can also be either Berdan or Boxer primed depending on the country manufacturing it. The U.S. military alone has over 25 variations of the fifty caliber that are known. The variations range from the M858 plastic tracer to the M903 tungston Armor Penetrator called the SLAP round .

Although the fifty caliber has mostly been utilized as an antiaircraft/ anti-armored vehicle round, in the late sixties- early seventies the military wanted to once again expand the uses of the fifty caliber round and use it as a anti-personnel round as well. Even though the .50 had been used in limited instances as a “sniper” round in the Korean and Vietnam war, the military wanted in essence to make a long range “shotgun” out of the .50 Browning. Some of the first of many experiments were conducted by Colt Industries Military Arms Division. Colt attempted to make a single fifty caliber round into a multiple projectile round by reducing the .50 to five .30 projectiles with copolymer and encasing the rounds in a plastic type wrapping, called the Salvo Squeeze Bore System. The .50/. 30 Squeeze Bore system theory was that a single Browning M2 Machine Gun with a cyclic rate of 600 rounds per minute would be capable of firing 3,000 anti-personnel projectiles per minute when loaded with the Squeeze Bore rounds. (See N, O, & P in center spread) The only modifications that would have to be made to the Browning M2 would be a special barrel in which the front portion was a smooth, tapered section, which was designed to reduce the various projectiles and then separate the projectiles upon exiting the barrel. The Squeeze Bore cartridge weighed 1750 grains and was 5.325 in length with 5 projectiles weighing between 132 to 138 grains apiece. The approximate velocity of the projectiles were; 1st bullet 3000ft. /sec, 2nd. Bullet 2800ft. /sec, 3rd bullet 2600 ft./sec, 4th bullet 2400ft. /sec, 5th bullet 2200ft. /sec. and had a spread of 15.7 inches and a range in excess of 500 yards. The .50cal Squeeze Bore system was used for a brief time during Viet Nam by the Navy Seals but was only “ moderately successful” according to Colt and the DOD. Only 100,000 rounds were ever deployed.

The fifty caliber round (12.7×99) is still one of the most widely used rounds to date and it’s tactical applications have proven to be limitless in battle. It most recently was proclaimed one of the most effective sniper rounds during Desert Storm where some of the first “Slap” (Saboted Light Armor Penetrator) M903 rounds were deployed in battle on armored vehicles at ranges up to one mile away and more. Shortly after Desert Storm the 50 BMG became very popular with civilian shooters due to it’s long range capabilities and sales of .50 caliber riffles such as the Barrrett “Light Fifty” 82 A1 doubled. The 50 BMG, with ranges over a mile and muzzle velocities in excess of 4500 fps will undoubtedly remain one of the most popular cartridges even into the 21st century.

M1 Tracer: (E) Intended to permit visible observation of the bullets in-flight from the Browning ground machine gun to the point of impact. Intended for training purposes only. It was generally replaced with the M17 .50 caliber tracer in combat. This cartridge is 5.45 inches long and can be identified by a red bullet tip. The bullet consists of a gilding metal or gilding- metal- clad steel jacket, a lead antimony slug which fills the forward end of the jacket, and the tracer and igniter compositions which fill the balance. Unlike the bullets for armor piercing and ball cartridges, this bullet is cylindrical to the base, which is open to permit the propelling charge to ignite the tracer composition. The overall length of the bullet is 2.40 inches. The trace begins at 250 ft from the barrel and the range of the trace is 1,600 to 1,800 yards. The weight is 1785, chamber pressure 52,000 and travels at a velocity of 2700 fps. Approximate range 6,132yds.

M10 Tracer: (D) This cartridge is for observation of fire in all .50 caliber aircraft machine guns. The M10 tracer serves the same purposes as the M1 tracer. The cartridge is 5.45 inches long and can be identified by an Orange bullet tip. The description and exterior ballistics for the M10 tracer are applicable with the M1 with the exception of the M10 has a dim or invisible trace for the first 225yds of flight followed by a bright trace for 1,600 yds.

M17 Tracer: (C) This cartridge was be used as a substitute for the M20 API-T but did not have as great of penetration. This type of ammunition was designed to replace the M1 tracer cartridge. The round is 5.45 inches long and can be identified by a brown bullet tip. The tips of the bullets were painted maroon prior to 1952. The description and exterior ballistics for the M17 tracer are applicable with the M1 and M10 with the exception of the M17 has a bright trace for approximately 2,450 yds. The M17 has been manufactured since 1950.

M21 Tracer: This cartridge is intended for the .50 aircraft machine guns for use in combat. When viewed from the front, its trace due to a certain igniter composition instead of tracer composition such as is used in the M1. The trace is three times as brilliant at that from the M1 tracer. The M21 also has some incendiary effect at 150 to 350 yds, but is negligible at 600 yds. The cartridge is 5.45 inches long and can be identified by a red bullet tip. The description and exterior ballistics of the M21 is comparable to the M1, M10and the M17.

M48A1 spotter: This cartridge is used in the M8 .50 caliber-spotting rifle for spotting the target for the gunner of the 106mm, M40. The brass cartridge case is 4.53 inches long. It contains approximately 117.5 grains of extruded single-base tubular propellant and a percussion primer. The case is crimped to the bullet by means of a 360o roll crimp. The case is fitted with a flash tube 0.984-inch long and an orifice diameter of 0.093 inch. The flash tube extends from the primer vent toward the mouth of the case. This cartridge can be identified by a yellow tip with a red annulus to the rear. The bullet has a gilding-metal jacket containing an incendiary charge in an aluminum alloy container and a tracer and igniter composition in a steel container. Upon contact with a target, the bullet will produce a flash and a light puff of smoke. The trace begins at a distance not greater than 100 yards from the muzzle and continues to a distance of approximately 1,500 yards. The bullet is 2.70 inches long.

M8Ball armor-piercing incendiary: (F) The API M8 cartridge was designed to replace the M1 incendiary and the M2 armor-piercing cartridge. This cartridge is 5.45 inches long and can be identified by an aluminum bullet tip. The bullet contains the same core as the M2 armor-piercing bullet but the point filler is replaced by an incendiary composition and the bullet also contains a lead antimony base filler. The length of the bullet is 2.31 inches long and is a 1764-grain with a muzzle velocity of 2910fps. The penetration ability is almost equal to that of the M2 armor-piercing bullet. The M2 will penetrate 7/8-inch thick armor plate at impact at 100 yards. Approximate range of the M2 is 7,117 yards.

M20 Armor-piercing-incendiary-tracer: (J) The APIT M20 cartridge is similar to the M8 armor-piercing-incendiary cartridge with the addition of a tracer element. The use of this cartridge makes tracer ammunition unnecessary in machine gun belts. The cartridge is 5,45 inches long and can be identified by a red and aluminum bullet tip. The bullet is similar to the M8 armor-piercing-incendiary bullet but also contains a tracer element. A visible trace begins at approximately 100 yards to 250 yards, were it changes to a bright trace which continues to approximately 1,750 yards. It also has a penetration of 7/8-inch armor plate at 100 yards. Approximate range of the M20 is 7,117 yards.

M2 Ball: (A) This cartridge is 5.45 inches long. The tip of the bullet is unpainted. The bullet consists of a gilding metal jacket, a soft steel core, and a point filler of lead antimony alloy. The bullet is boattailed and is 2.31 inches long. The M2 is an 1813-grain and has an approximate range of 8,140 yards. The cartridge is intended for use against personnel or unarmored targets.

M33 Ball: (B) This cartridge was designed to replace the M2 ball cartridge and to duplicate the ballistics of an inert API M8 cartridge. The M33 ball is designed for general use where tracer, incendiary or armor penetration characteristics are not important considerations. The cartridge is 5.45 inches long. The external appearance of this round is the same as the M2 ball. The bullet consists of a gilding-metal jacket or gilding metal clad steel, a soft steel core, and a loose or pelletized sodium carbonate monohydrate point filler. The bullet is 2,31 inches long and a boattailed base. The M33 is 1762 grain and has an approximate range of 8,140 yards. The cartridge is intended for use against personnel or unarmored targets.

M1 Incendiary: (H) This cartridge is 5.45 inches long. It can be identified by a light blue bullet tip, and by a second knurled cannelure rolled into the bullet jacket. The bullet is similar in size and shape to the M2 armor-piercing bullet. The M1 incendiary bullet consists of a gilding-metal jacket, a hollow cylindrical steel body, a lead antimony base slug, and a point filler of incendiary composition. The bullet has a boattailed base and is 2.09 inches long. The M1 incendiary is 1744-grain bullet and a velocity of 2950 fps.

M23 Incendiary: (K) This cartridge is for use only in .50 caliber aircraft machine guns. The M23 incendiary cartridge has a higher velocity than the M1 incendiary cartridge and is more effective as an incendiary against aviation kerosene. The M23 is 5.45 inches long and can be identified by a medium blue with a light blue annulus to the rear of the bullet. The bullet is similar in external appearance to the incendiary M1 bullet. The M23 consists of a gilding metal jacket; a gilding metal clad steel container, a lead antimony base slug, and a point filler of incendiary composition. The weight of the incendiary composition is greater than that in the M1. The bullet is 2.29 inches long and has a square base. The M23 incendiary is 1581 grain and has a velocity of 3400 fps.

M2 Dummy: (Q) This cartridge is for use in all .50 caliber machine guns for training purposes. The M2 dummy cartridge is also used for testing the mechanism of weapons. The cartridge is 5.45 inches long. The case may be made of steel or brass. This cartridge can be identified by three holes drilled in the side of the case and an empty primer pocket. The bullet has a gilding metal or gilding metal clad steel jacket making it lighter than older types which had a steel core and lead point filler.

M2 Armor- piercing: (I) The M2I is for use in all .50 caliber machine guns. It is 5.45 inches long and can be identified by a Black bullet tip. The M2 armor-piercing cartridge is designed for use against armored aircraft, armored vehicles, concrete shelters, and similar bullet resisting targets. The bullet consists of a gilding-metal jacket, a hardened core of manganese-molybdenum steel, and a point filler of lead antimony. The overall length of the bullet is 2.31 inches. The bullet has a boattailed base. The M2AP has a muzzle velocity of 2930, max. range of 8,140 yards and will penetrate 1 inch of armor plate at 200 yards.

M1 Blank: The M1 blank cartridge is used to simulate firing during training exercises. The cartridge is 3.91 inches long and is identifies by the absence of a bullet and has a crimped cartridge case mouth. Weight is 917 grains.

M1A1 Blank: (R) The M1A1 blank cartridge is used to simulate firing during training exercises in conjunction with the M19 blank ammunition firing attachment. The cartridge length is 3.19 and is identified by the absence of a bullet. The M1A1 differs from the M1 blank in that the M1A1 has a rosette crimp at the mouth. Also the M1A1 is loaded with Dupont Hi Skor 700X propellant. Weight is 915 to 955 grains.

MK211Armor- Piercing Incendiary: (G) The MK211 armor-piercing incendiary is used to provide improved penetration performance against enemy personnel and light armor vehicles. The cartridge is 5.45 inches long and identified by a green bullet tip. The projectile is 671 grains, consists of a brass jacket surrounding a steel body and tungsten core with incendiary and 13 grains of high explosive charges. The MK211is 1765 grain has a muzzle velocity of 2910 fps.

M903 Saboted Light Armor Penetrator (SLAP): (M) The M903 cartridge is used to maximize penetration of light armored targets. The cartridge is 5.45 inches long and can be identified by an amber sabot. The projectile is 355 grain, reduced to .30 caliber and is made of tungsten wrapped in a “plastic” sabot. Because of the reduced size and weight of the projectile it is capable of a muzzle velocity of 4000 fps and an extremely flat trajectory allowing it superior penetration over regular .50 AP. The maximum effective range is 4921.5feet and it is capable of penetration of 3/4 inch of hard armor.

M962 Saboted Light Armor Penetrator tracer: (L) The M962 cartridge is to be used in conjunction with the M903 light armor penetrator to permit visible observation of the bullets in flight to the point of impact. The cartridge is 5.45 inches long and can be identified by a red sabot. The projectile is 350-360 grains, reduced to .30 caliber and is made of tungsten wrapped in a “plastic” sabot with a tracer element. Total cartridge weight is 1466 grains and has a muzzle velocity of 4000 fps. The maximum range is 4921.5 feet.

M860 Plastic Practice Tracer: The M860 cartridge is intended for scaled range training to permit visible observation of the bullet’s flight path or trajectory to the point of impact. It was designed to be a low cost alternative ammunition for training only. The cartridge is 5.2 inches long and can be identified by a red bullet tip and a blue plastic case which are molded into one piece with high density polyethlene plastic. Total cartridge weight is 460 grains and has a muzzle velocity of 2790fps. The maximum range is 750 yards.

M858 Plastic Practice Ball: The M858 cartridge is intended for scaled range training purposes. The cartridge is 5.2 inches long and can be identified by a blue bullet and case molded into one piece with high-density polyethlene plastic. Total cartridge weight is 460 grains and has a muzzle velocity of 2790fps. The maximum range is 750 yards.