Editing M2 Browning (section)

==Design details==
{{More citations needed section|date=November 2021}}

The Browning M2 is an [[air-cooled]], [[Belt (firearm)|belt-fed]] machine gun. The M2 fires from a [[closed bolt]], operated on the [[short recoil]] principle. The M2 fires the .50 BMG cartridge, which offers longer range, greater accuracy, and immense [[stopping power]]. The closed bolt firing cycle made the M2 usable as a synchronized machine gun on aircraft before and during World War II, as on the early versions of the [[Curtiss P-40]] fighter. The M2 is a scaled-up version of John Browning's [[M1917 Browning machine gun|M1917 .30 caliber machine gun]].

===Features===
The M2 has varying cyclic rates of fire, depending on the model. The M2HB air-cooled ground gun has a cyclical rate of 450–575 rounds per minute.<ref>{{harvnb|Dunlap|1948|pp=310–311}}: "The official rate during WWII was 450–575&nbsp;rpm, but it was extremely rare to encounter an M2HB that exceeded 550&nbsp;rpm."</ref> The early M2 water-cooled AA guns had a cyclical rate of around 450–600&nbsp;rpm.<ref>{{cite web |url=http://www.navweaps.com/Weapons/WNUS_50cal-M2_MG.htm |title=USA 0.50"/90 (12.7 mm) M2 Browning Machine Gun |first=Tony |last=DiGiulian |date=2007 |website=Navweaps.com |url-status=dead |archive-url=https://web.archive.org/web/20081102231537/http://www.navweaps.com/Weapons/WNUS_50cal-M2_MG.htm |archive-date=2008-11-02}}</ref> The AN/M2 aircraft gun has a cyclic rate of 750–850&nbsp;rpm; this increases to 1,200&nbsp;rpm for AN/M3 aircraft guns. These maximum rates of fire are generally not achieved in use, as sustained fire at that rate will wear out the bore within a few thousand rounds, necessitating replacement. In addition to full automatic, the M2HB can be selected to fire single shots, fire slowly at less than 40 rounds per minute, or fire rapidly for more than 40 rounds per minute. Slow and rapid firing modes use 5–7 round bursts with different lengths of pause between bursts.<ref>{{cite web |url=http://m2hb.net/manuals/fm23_65.pdf |title=FM 23-65: Browning Machine Gun Caliber .50 HB, M2 |date=December 2002 |website=U.S. Department of the Army |url-status=dead |archive-url=https://web.archive.org/web/20110430022123/http://m2hb.net/manuals/fm23_65.pdf |archive-date=2011-04-30}}</ref>

[[File:M2 - 24th MEU.jpg|thumb|left|A U.S. Marine mans a .50 caliber machine gun as part of a security force during a training exercise with the 24th Marine Expeditionary Unit in November 2002.]]
The M2 has an effective range of {{convert|1830|m|yard}} and a maximum effective range of {{convert|2000|m|yard}} when fired from the [[M3 tripod]]. In its ground-portable, crew-served role as the M2HB, the gun itself weighs {{convert|84|lb|kg}} and the assembled M3 tripod another {{convert|44|lb|kg}}. In this configuration, the V-shaped "butterfly" trigger is located at the very rear of the weapon with a "spade handle" handgrip on either side of it and the bolt release in the center. The spade handles are gripped and the butterfly trigger is depressed with one or both thumbs. Recently, new rear buffer assemblies have used squeeze triggers mounted to the handgrips, doing away with the butterfly triggers.

When the bolt release is locked down by the bolt latch release lock on the buffer tube sleeve, the gun functions in fully automatic mode. Conversely, the bolt release can be unlocked into the up position resulting in single-shot firing (the gunner must press the bolt latch release to send the bolt forward). Unlike virtually all other modern machine guns, it has no safety (although a sliding safety switch has recently been fielded to USMC armorers for installation on their weapons and is standard-issue for the U.S. Army for all M2s). Troops in the field have been known to add an improvised safety measure against accidental firing by slipping an expended shell casing under the butterfly trigger.<ref>{{cite web |url=http://mcdetflw.tecom.usmc.mil/usmc-mp2006/READ%20AHEAD/ADVANCE%20COURSE%20READ%20AHEAD/ADVANCE%20COURSE%20OUTLINES/Crew%20Served%20Weapons%20lesson%20plan.doc |title=Lesson Plan: Crew Served Weapons |date=25 June 2007 |website=United States Marine Corps |url-status=dead |archive-url=https://web.archive.org/web/20090227120628/http://mcdetflw.tecom.usmc.mil/usmc-mp2006/READ%20AHEAD/ADVANCE%20COURSE%20READ%20AHEAD/ADVANCE%20COURSE%20OUTLINES/Crew%20Served%20Weapons%20lesson%20plan.doc |archive-date=2009-02-27}}</ref> The upgraded M2A1 has a manual trigger block safety.

[[File:Twin M2HB machine gun.jpg|thumb|upright|Twin M2HB machine gun during a pre-action calibration fire (PACFIRE) exercise in May 2005]]
Because the M2 was designed to operate in many configurations, it can be adapted to feed from the left or right side of the weapon by exchanging the belt-holding pawls, and the front and rear cartridge stops (three-piece set to include link stripper), then reversing the bolt switch. The operator must also convert the top-cover belt feed slide assembly from left to right-hand feed as well as the spring and plunger in the feed arm. This will take a well-trained individual less than two minutes to perform.

The charging assembly may be changed from left to right-hand charge. A right-hand charging handle spring, lock wire, and a little "know-how" are all that is required to accomplish this. The M2 can be battle-ready and easily interchanged if it is preemptively fitted with a retracting slide assembly on both sides of the weapon system. This eliminates the need to have the weapon removed from service to accomplish this task.

At some point during World War II, the Frankford Arsenal developed a [[squeeze bore]] version of the M2HB which reduced the bullet size from .50 to .30 caliber.<ref name="WeaponsMan">{{cite web |title=Exotic Barrels Part 1: Squeeze Bores |url=http://weaponsman.com/?p=21443 |website=WeaponsMan.com |access-date=18 July 2018 |archive-url=https://web.archive.org/web/20180709035248/http://weaponsman.com/?p=21443 |archive-date=9 July 2018 |url-status=live}}</ref>

===Ammunition===
There are several different types of ammunition used in the M2HB and AN aircraft guns. From [[World War II]] through the [[Vietnam War]], the Browning was used with standard ball, armor-piercing (AP), armor-piercing incendiary (API), and armor-piercing incendiary tracer (APIT) rounds. All .50 ammunition designated "armor-piercing" was required to completely perforate {{convert|0.875|in|mm}} of hardened steel armor plate at a distance of {{convert|100|yd|m}} and {{convert|0.75|in|mm}} at {{convert|547|yd|m}}.<ref name="Barnes, Frank C. 1989 p.432">{{cite book |last=Barnes |first=Frank C. |date=1989 |title=Cartridges of the World |chapter=U.S. Army .50 BMG Cartridge Specifications |publisher=DBI Books |page=432 |isbn=0-87349-033-9}}</ref> The API and APIT rounds left a flash, report, and smoke on contact, useful in detecting strikes on enemy targets; they were primarily intended to incapacitate thin-skinned and lightly armored vehicles and aircraft, while igniting their fuel tanks.{{sfn|Dunlap|1948|pp=311–312}}

Current ammunition types include M33 Ball (706.7 grain) for personnel and light material targets, M17 tracer, M8 API (622.5 grain), M20 API-T (619 grain), and M962 SLAP-T. The latter ammunition along with the M903 SLAP (Saboted Light Armor Penetrator) round can perforate {{convert|1.34|in|mm}} of FHA (face-hardened steel plate) at {{convert|500|m|yd}}, {{convert|0.91|in|mm}} at {{convert|1200|m|yd}}, and {{convert|0.75|in|mm}} at {{convert|1500|m|yd}}. This is achieved by using a {{convert|0.30|in|mm|adj=mid|-diameter}} tungsten penetrator. The SLAP-T adds a tracer charge to the base of the ammunition. This ammunition was type classified in 1993.{{cn|date=February 2023}}

[[File:US Navy 070821-F-8678B-034 Machinery Repairman Fireman Edward O. Pastoral mans a M2 .50 caliber machine gun.jpg|thumb|M2 with blank-firing adapter]]
When firing blanks, a large [[blank-firing adapter]] (BFA) of a special type must be used to allow the recoil-operated action to cycle. This functions on the principle of a [[recoil booster]], to increase the recoil force acting on the short recoil action. This is the exact antithesis of a [[muzzle brake]]. Without this adaptor, the reduced-charge blank cartridge would develop too little recoil to cycle the action fully. The adapter is very distinctive, attaching to the muzzle with three rods extending back to the base. The BFA can often be seen on M2s during peacetime operations.