Question: What cartridge was developed in 1910 and is currently used in the M2 machine gun? 
Context: The M205 Lightweight Tripod for Heavy Machine Guns is the replacement for the current M3 tripod in support of the M2 machine gun and Mk 19 grenade launcher used in the United States armed forces.  The soldier will experience less weight burden with the M205 Lightweight Tripod than with the standard M3 Tripod (50.3 lb , including the pintle and T&E), and will be able to take advantage of the enhanced tripod’s integrated traverse and elevation mechanism for quicker, more accurate target engagement. The M2 Machine Gun or Browning .50 Caliber Machine Gun is a heavy machine gun designed toward the end of World War I by John Browning.  Its design is similar to Browning's earlier M1919 Browning machine gun, which was chambered for the .30-06 cartridge.  The M2 uses the much larger and much more powerful .50 BMG cartridge, which was developed alongside and takes its name from the gun itself (BMG standing for "Browning Machine Gun").  It has been referred to as "Ma Deuce", in reference to its M2 nomenclature.  The design has had many specific designations; the official designation for the current infantry type is Browning Machine Gun, Cal.  .50, M2, HB, Flexible.  It is effective against infantry, unarmored or lightly armored vehicles and boats, light fortifications and low-flying aircraft.  The M2 has been produced longer than any other machine gun. The Canadian Machine Gun Corps (CMGC) was an administrative corps of the Canadian Army.  It was part of the Canadian Expeditionary Force sent to France during World War I.  The Canadian Permanent Machine Gun Brigade was organized in the Permanent Force on 3 November 1919.  The Canadian Permanent Machine Gun Brigade was redesignated the Royal Canadian Permanent Machine Gun Brigade on 16 June 1921.  The Royal Canadian Permanent Machine Gun Brigade was disbanded on 1 November 1923.  The Canadian Machine Gun Corps donated a wall plaque at St. George's Church in Ypres. The M85 is a heavy machine gun firing .50 BMG ammunition that was used primarily for turreted applications in armored fighting vehicles.  It was intended to replace the venerable M2 machine gun with a smaller and much lighter weapon, suitable for use inside fighting vehicle, as opposed to only on external mounts.  It was used on the M60 series of tanks and the LVTP-7 amphibious landing vehicle. The .50 Browning Machine Gun (.50 BMG, 12.7×99mm NATO and designated as the 50 Browning by the C.I.P.) is a cartridge developed for the Browning .50 caliber machine gun in the late 1910s.  Entering service officially in 1921, the round is based on a greatly scaled-up .30-06 cartridge.  Under STANAG 4383, it is a standard cartridge for NATO forces as well as many non-NATO countries.  The cartridge itself has been made in many variants: multiple generations of regular ball, tracer, armor-piercing (AP), incendiary, and saboted sub-caliber rounds.  The rounds intended for machine guns are linked using metallic links. The French St. Étienne Mle 1907 (French: "Mitrailleuse Mle 1907 T" ) was a gas operated air-cooled machine gun in 8mm Lebel which was widely used in the early years of the First World War.  The "St.Etienne Mle 1907" was not derived from the Hotchkiss machine gun.  Instead it was an entirely different gas operated blow-forward design borrowed from the semi-automatic Bang rifle of 1903.  This Bang system was first transposed in 1905 to the French Puteaux APX Machine Gun which soon proved to be unsatisfactory.  Then, two years later, the Mle 1907 "St-Etienne" machine gun followed as an improved redesign of the "Puteaux" machine gun.  However the Mle 1907 "Saint Etienne" was only a partial redesign : the original blow-forward gas piston, rack-and-pinion system, and bolt mechanism of the Mle 1905 " Puteaux" machine gun had all been kept only slightly modified inside the newer weapon.  Eventually a total of over 39,700 "St-Etienne" Mle 1907 machine guns were manufactured between 1908 and late 1917.  They were widely used by French infantry during the early part of World War I until their replacement by the distinctly more reliable Hotchkiss M1914 machine-gun. The 7.62×45mm (designated as the 7,62 × 45 by the C.I.P.) is a rimless bottlenecked intermediate rifle cartridge developed in Czechoslovakia.  It is fired by the Czech vz.  52 rifle, Vz.  52 machine gun and ZB-530 light machine gun.  The round was later dropped from use when the Czech converted to the standard Warsaw Pact round, the 7.62×39mm (fired by vz.  52/57 rifle and vz.  52/57 light machine gun).  Its muzzle velocity and muzzle energy are slightly higher than that of the 7.62×39mm cartridge. Type 3 (三式, San-Shiki) was a Japanese Navy aircraft machine gun used during World War II.  It was based on the American M2 Browning machine gun but used the 13.2x96mm Hotchkiss cartridge. The T24 machine gun was a copy of the MG 42 developed during World War II as a possible replacement for the Browning Automatic Rifle & M1919A4 for infantry squads, the new version being adapted for the .30-06 cartridge.  Saginaw Steering Gear constructed a working prototype designated as the T24 machine gun which could also be used on an M2 Tripod.  However, the realization that the .30-06 cartridge might be too long for the gun's mechanism to easily cope with, and most notably a design flaw in the prototype resulted in the discarding of the project. The Degtyaryov machine gun (Russian: Пулемёт Дегтярёвa Пехотный "Pulemyot Degtyaryova Pekhotny" "Degtyaryov's infantry machine gun") or DP-28 is a light machine gun firing the 7.62×54mmR cartridge that was used primarily by the Soviet Union starting in 1928.  The DP machine gun was supplemented in the 1950s by the more modern RPD machine gun and entirely replaced in Soviet service by the general purpose PK machine gun in the 1960s.
Answer: .50 BMG