The M4 carbine is a shorter and lighter variant of the M16A2 assault rifle. The M4 is air-cooled, direct impingement gas-operated, magazine-fed carbine, it has a 14.5 in a telescoping stock. The M4 carbine is extensively used by the United States Armed Forces and is replacing the M16 rifle in United States Army and United States Marine Corps combat units as the primary infantry weapon and service rifle; the M4 is capable of mounting the M203 and M320 grenade launchers. The distinctive step in its barrel is for mounting the M203 with the standard hardware; the M4 has semi-automatic and three-round burst firing modes, while the M4A1 has semi-automatic and automatic firing modes. Following the adoption of the M16 rifle, carbine variants were adopted for close quarters operations; the CAR-15 family of weapons served through the Vietnam War. However, these rifles had design issues, as "the barrel length was halved" to 10 inches, which "upset the ballistics", reducing its range and accuracy and leading "to considerable muzzle flash and blast, so that a large flash suppressor had to be fitted".
"Nevertheless, as a short-range weapon it is quite adequate and thus, its caliber, is classed as a submachine gun." In 1984, Colt began work on a new carbine design called the XM4 combining the best features of the Colt Commando and the M16A2 rifles. In 1984, the first model was made, it was tested in May 1985; the first models had an upper receiver with an A1 sight, were given a shorter 11.5-inch barrel, but ones were given a longer 14.5-inch barrel for the bayonet and the M203 Grenade Launcher. The second model was made in May 1986, it was tested from May 1986 though May 1987; the extended barrel improved the XM4's ballistics, reduced muzzle blast and gave the XM4 the ability to mount a bayonet and the M203 grenade launcher. The XM4 was given the cartridge deflector, as well as other minor refinements. In May 1991, the XM4 was renamed to the M4, Colt made a manual; the M4 was accepted into service by the U. S. military in 1994, first saw action in the hands of U. S. troops deployed to Kosovo in 1999 in support of the NATO-led KFOR peacekeeping force.
It would subsequently be used by U. S. forces during the Global War on Terrorism, including Operation Enduring Freedom and Operation Iraqi Freedom. In the U. S. Army, the M4 had replaced M16A2s as the primary weapon of forward deployed personnel by 2005; the M4 carbine replaced most submachine guns and selected handguns in U. S. military service, as it fires more effective rifle ammunition that offers superior stopping power and is better able to penetrate modern body armor. The United States Marine Corps has ordered its officers and staff non-commissioned officers to carry the M4 carbine instead of the M9 handgun; this is in keeping with the Marine Corps doctrine, "Every Marine a rifleman". The Marine Corps, chose the full-sized M16A4 over the M4 as its standard infantry rifle. United States Navy corpsmen E5 and below are issued M4s instead of the M9. While ordinary riflemen in the Marine Corps were armed with M16A4s, M4s were fielded by troops in positions where a full-length rifle would be too bulky, including vehicle operators and fireteam and squad leaders.
As of 2013, the U. S. Marine Corps had 80,000 M4 carbines in their inventory. By July 2015, major Marine Corps commands were endorsing switching to the M4 over the M16A4 as the standard infantry rifle, just as the Army had done; this is because of the carbine's lighter weight, compact length, ability to address modern combat situations that happen within close quarters. Approval of the change would move the M16 to support personnel, while armories had the 17,000 M4s in the inventory needed to outfit all infantrymen who needed one. In October 2015, Commandant Robert Neller formally approved of making the M4 carbine the primary weapon for all infantry battalions, security forces, supporting schools in the U. S. Marine Corps; the switch was to begin in early 2016 and be completed by September 2016. In December 2017, the Marine Corps revealed a decision to equip every Marine in an infantry squad with the M27, replacing the M4 in that part of the service. MARSOC will retain the M4, as its shorter barrel is more suited to how they operate in confined spaces.
On 1 July 2009, the U. S. Army took complete ownership of the M4 design; this allowed companies other than Colt to compete with their own M4 designs. The Army planned on fielding the last of its M4 requirement in 2010. On 30 October 2009, Army weapons officials proposed a series of changes to the M4 to Congress. Requested changes included an electronic round counter that records the number of shots fired, a heavier barrel, replacing the direct impingement system with a gas piston system; the benefits of this, have come under scrutiny from both the military and civilian firearms community. According to a PDF detailing the M4 Carbine improvement plans released by PEO Soldier, the direct impingement system would be replaced only after reviews were done comparing the direct impingement system to commercial gas piston operating system to find out and use the best available operating system in the U. S. Army's improved M4A1. In September 2010, the Army announced it would buy 12,000 M4A1s from Colt Firearms by the end of 2010, would order 25,000 more M4A1s by early 2011.
The service branch planned to buy 12,000 M4A1 conversion kits i
The Picatinny Arsenal is an American military research and manufacturing facility located on 6,400 acres of land in Jefferson and Rockaway Township in Morris County, New Jersey, United States, encompassing Picatinny Lake and Lake Denmark. The Arsenal is the headquarters of the United States Army Armament Research and Engineering Center, it is known for developing the ubiquitous Picatinny rail, as well as being the army's center of expertise for small arms cartridge ammunition. The facility was founded in 1880 as the Picatinny Powder Depot. Soon afterward, the navy acquired a portion of the arsenal to establish the Lake Denmark Powder Depot known as Lake Denmark Naval Ammunition Depot, it manufactured gunpowder until after World War I, at which time the facility began producing heavy munitions and grew more involved in research and development activities. During World War II Picatinny was a major large-caliber-round loading plant with 18,000 employees. Today, the facility develops new technologies for the US Armed Forces and builds various munitions and armor systems.
Picatinny Arsenal is home to the US Army Explosive Ordnance Disposal Technology Directorate. This group is responsible for the creation of tools and procedures for US Army EOD personnel; some of their more recent inventions were the use of weapons on a robot platform and the SWORDS robot. Their building has been renamed in honor of one of their deceased soldiers, SFC Scott "Smitty" Smith, killed in Iraq in July 2006. Prior to the American Civil War gunpowder was stored by the United States Army at various powder facilities throughout the eastern United States. Many of these facilities were located in the South and were confiscated by the Confederate States of America at the beginning of the war; the federal government began looking for a central storage depot to be located near the large cities of the northeast. The United States War Department established the Dover Powder Depot on September 6, 1880. Four days it changed the name to the "Picatinny Powder Depot". A deed dated June 26, 1880 records the first land purchase for the future Picatinny Arsenal.
George E. Righter transferred 1,195.8 acres centered on Lake Picatinny to the United States government in return for $35,874.00. This area, afterwards known as the Middle Forge Tract because of the forge located there during the Revolutionary War, became the central area of the arsenal. In 1880 and 1881, the government purchased tracts from Uel H. Wiggins, Edward C. Fiedler and other and Michael Doland, John E. Kindred; these initial purchases, including the Middle Forge Tract, covered 1,866.13 acres and cost a total of $62,750.00. At the same time, the government gave $200.00 to Lewis Spicer and his wife for a 50-foot strip on which to construct a road from Spicertown to the powder depot. In 1891, the army transferred 315 acres bordering Lake Denmark to the navy; the arsenal was located in a valley between two sets of hills that might shield the surrounding countryside from any accidental explosions. In 1907, the army altered the name to the "Picatinny Arsenal" and established its first powder factory on the site.
While continuing to produce munitions, the arsenal moved into research and development work with the start of a school to instruct officers in weaponry sciences in 1911, the establishment of testing and control laboratories during the World War I era, the beginning of a small, experimental plant for the design and development of artillery ammunition in 1919. In 1921, the arsenal took over responsibility for experimental work on fuzes. On July 10, 1926, lightning started a fire; as a result, several million pounds of explosives detonated over a period of three days. This left not only military and civilian casualties as well; the value of ammunition destroyed was the equivalent of a billion dollars in present-day terms. As a result of a full-scale Congressional investigation, Congress directed the establishment of the Armed Forces Explosives Safety Board to provide oversight on every aspect of explosives under the control of the US Armed Forces; the review led to creation of a remote, safe depot to serve the West Coast, which became the Hawthorne Naval Ammunition Depot, in Nevada, opened in 1928.
The arsenal continued to realize its potential as a research and development facility in the years between the two world wars. Major accomplishments of this period included better methods for storing smokeless powder, improved processing of cyclonite, the discovery of a new explosive known as haleite but known as Ednatol. Over the years, the army continued to make small purchases to round out arsenal boundaries, but the next major expansion came in 1941, just before the United States entered World War II. At this time, the army purchased the land between the Cannon Gates and the present main entrance near Route 15; this included an unincorporated village in Rockaway Township. Spicertown had declined from a thriving 19th-century community of small but profitable farms to a rather depressed area in 1941. Many of the residences housed military families until the early 2000s. Near Parker Road is property acquired from the estate of John E. Larson for $16,000.00. The purchase price included 24 acres of land.
Another former Spicertown property consisting of 12 acres cost the government $19,769.00. Property on the opposite side of Parker Road was acquired from Helen Jane Larsen with 1.5 acres for $10,534.00, as well as the former home of Clar
An O-ring known as a packing, or a toric joint, is a mechanical gasket in the shape of a torus. The O-ring may be used in static applications or in dynamic applications where there is relative motion between the parts and the O-ring. Dynamic examples include hydraulic cylinder pistons. Static applications of O-rings may include fluid or gas sealing applications in which: the O-ring is compressed resulting in zero clearance, the O-ring material is vulcanized solid such that it is impermeable to the fluid or gas, the O-ring material is resistant to degradation by the fluid or gas. O-rings are one of the most common seals used in machine design because they are inexpensive, easy to make and have simple mounting requirements, they have been tested to seal up to 5000 psi of pressure. The maximum recommended pressure of an O-ring seal depends on the seal hardness and gland clearance. O-rings can be produced by injection molding, pressure molding or transfer molding; the first patent for the O-ring, is dated May 1896 as a Swedish patent.
J. O. Lundberg, the inventor of the O-ring, received the patent; the US patent for the O-ring was filed in 1937 by a 72-year-old Danish-born machinist, Niels Christensen. Soon after migrating to the United States in 1891, he patented an air brake system for streetcars. Despite his legal efforts, his intellectual property rights were passed from company to company until they ended up at Westinghouse. During World War II, the US government commandeered the O-ring patent as a critical war-related item and gave the right to manufacture to other organizations. Christensen received a lump sum payment of US$75,000 for his efforts. Litigation resulted in a $100,000 payment to his heirs 19 years after his death. O-rings are available in various inch standard sizes. Sizes are specified by the cross section diameter. In the US the most common standard inch sizes are per SAE AS568C specification. ISO 3601-1:2012 contains the most used standard sizes, both inch and metric, worldwide; the UK has standards sizes known as BS sizes ranging from BS001 to BS932.
Several other size specifications exist. Successful O-ring joint design requires a rigid mechanical mounting that applies a predictable deformation to the O-ring; this introduces a calculated mechanical stress at the O-ring contacting surfaces. As long as the pressure of the fluid being contained does not exceed the contact stress of the O-ring, leaking cannot occur; the pressure of the contained fluid transfers through the incompressible O-ring material, the contact stress rises with increasing pressure. For this reason, an O-ring can seal high pressure as long as it does not fail mechanically; the most common failure is extrusion through the mating parts. The seal is designed to have a point contact between the sealing faces; this allows a high local stress, able to contain high pressure, without exceeding the yield stress of the O-ring body. The flexible nature of O-ring materials accommodates imperfections in the mounting parts, but it is still important to maintain good surface finish of those mating parts at low temperatures where the seal rubber reaches its glass transition temperature and becomes crystalline.
Surface finish is especially important in dynamic applications. A surface finish, too rough will abrade the surface of the O-ring, a surface, too smooth will not allow the seal to be adequately lubricated by a fluid film. In vacuum applications, the permeability of the material makes point contacts quite useless. Instead, higher mounting forces are used and the ring fills the whole groove. Round back-up rings are used to save the ring from excessive deformation Because the ring feels the ambient pressure and the partial pressure of gases only at the seal, their gradients will be steep near the seal and shallow in the bulk (opposite to the gradient of the contact stress See: Vacuum flange#KF.2FQF. High-vacuum systems below 10 − 9 Torr use nickel O-rings. Vacuum systems that have to be immersed in liquid nitrogen use indium O-rings, because rubber becomes hard and brittle at low temperatures. In some high-temperature applications, O-rings may need to be mounted in a tangentially compressed state, to compensate for the Gow-Joule effect.
O-rings come in a variety of sizes. Society of Automotive Engineers Aerospace Standard 568 specifies the inside diameters, cross-sections and size identification codes for O-rings used in sealing applications and for straight thread tube fitting boss gaskets. British Standard which are imperial sizes or metric sizes. Typical dimensions of an O-ring are internal dimension, outer dimension and thickness / cross section Metric O-rings are defined by the internal dimension x the cross section. Typical part number for a metric O-ring - ID x CS 2x1N70 = defines this O-ring as 2mm id with 1mm cross section made from Nitrile rubber, 70Sh BS O-rings are defined by a standard reference. O-ring selection is based on chemical compatibility, application temperature, sealing pressure, lubrication requirements, durometer and cost. Synthetic rubbers - Thermosets: Butadiene rubber Butyl rubber Chlorosulfonated polyethylene Epichlorohydrin rubber Ethylene propylene diene monomer: good resistance to hot water and steam, caustic potash solutions, sodium hydr
AR-15 style rifle
An AR-15 style rifle is a lightweight semi-automatic rifle based on the ArmaLite AR-15 design. ArmaLite sold the patent and trademarks to Colt's Manufacturing Company in 1959. After Colt's patents expired in 1977, Colt retained the trademark and is the exclusive owner of "AR-15" designation. An expanded marketplace emerged with many manufacturers producing their own version of the AR-15 design for commercial sale, they are referred to as modern sporting rifles by the US National Shooting Sports Foundation, a firearms industry trade association, by some manufacturers. Coverage of high-profile incidents where various versions of the rifle were involved uses the shorthand AR-15. AR-15 style rifles have become one of the "most beloved and most vilified rifles" in the United States, according to the New York Times; the rifle has been promoted as "America's rifle" by the National Rifle Association. They have been used in several mass shootings in the United States; the Public Safety and Recreational Firearms Use Protection Act restricted the Colt AR-15 and derivatives from 1994 to 2004, although it did not affect rifles with fewer features.
In 1956, ArmaLite designed a lightweight selective fire rifle for military use and designated it the ArmaLite Rifle model 15, or AR-15. Due to financial problems and limitations in terms of manpower and production capacity, ArmaLite sold the design and the AR-15 trademark along with the ArmaLite AR-10 to Colt's Manufacturing Company in 1959. In 1964, Colt began selling its own version with an improved semi-automatic design known as the Colt AR-15. After Colt's patents expired in 1977, an active marketplace emerged for other manufacturers to produce and sell their own semi-automatic AR-15 style rifles; some versions of the AR-15 were classified as "assault weapons" and banned under the Public Safety and Recreational Firearms Use Protection Act in 1994. This act expired in 2004. In 2009, the term "modern sporting rifle" was coined by the National Shooting Sports Foundation for its survey that year as a marketing term used by the firearms industry to describe modular semi-automatic rifles including AR-15s.
Today, nearly every major firearm manufacturer produces its own generic AR-15 style rifle. As Colt continues to own and use the AR-15 trademark for its line of AR-15 variants, other manufacturers must use their own model numbers and names to market their AR-15 style rifles for commercial sale. While most earlier breech-loading rifles had a single receiver housing both the trigger and reloading mechanism, an innovative feature of the AR-15 was modular construction to simplify substitution of parts and avoid need for arsenal facilities for most repairs of malfunctioning military rifles. A distinctive two-part receiver is used by both sporting AR-15 style rifles; as civilian ownership of AR-15 style rifles became sufficient to create a market for improvements, numerous manufacturers began producing one or more "improved" modules, assemblies, or parts with features not found on factory rifles. Due to the vast assortment of aftermarket parts and accessories available, AR-15 style rifles have been referred to as "the Swiss Army knife of rifles," "Barbie Dolls for Guys," or "LEGOs" for adults.
These more or less interchangeable modules are a defining characteristic of AR-15 style rifles. The lower receiver is the serial-numbered part defined as the firearm under United States law. A completed lower receiver is visually distinguished by the trigger guard ahead of the detachable pistol grip, behind the magazine well capable of holding detachable magazines; the lower receiver holds the trigger assembly including the hammer, is the attachment point for the buttstock. The lower receiver is attached to the upper receiver by two removable pins. Disassembly for cleaning or repair of malfunctions requires removal of these pins. Removal of the rear take-down pin allows the receiver to be opened by rotation around the forward pivot pin as a hinge; the upper receiver contains the bolt carrier assembly, is attached to the barrel assembly. Sights will be attached to the barrel assembly. A handguard encloses the barrel and a gas-operated reloading device using burnt powder gas vented from a hole in the barrel near the forward end of the handguard.
The handguard is attached to the upper receiver and may be attached to the barrel. The initial design included a tube to vent burnt powder gas back into the bolt carrier assembly where it expands in a variable volume chamber forcing the bolt open to eject the spent cartridge case. A buffer spring in the butt stock pushes the bolt closed picking up a new cartridge from the magazine; this direct gas impingement system has the disadvantage of venting un-burned smokeless powder residue into the receiver where it may accumulate in quantities causing malfunctions. A more recent alternative design has a metal operating rod pushing against the bolt carrier from a gas piston under the hand guard near the barrel port; this piston keeps the receiver cleaner by exhausting under the hand guard. While both the DGI and piston systems produce semi-automatic fire, an alternative un-ported barrel assembly includes a sliding hand guard connected to a rod moving the bolt by a pump action and eliminating semi-automatic fire.
Most rifles eject spent cartridges from the right side of the receiver away from right handed shooters who place the butt against the right shoulder while sighting with the right eye and using a finger of the right hand to pull the trigger. Right-side ejection is a disadvantage for the third of the population whose left eye is dominant, for the tenth of the population who are left handed, because hol
Squad automatic weapon
A squad automatic weapon section automatic weapon. Weapons used in this role are selective-fire rifles fitted with a bipod and heavier barrel to perform as light machine guns. Squad automatic weapons fire the same cartridge as the assault rifles or battle rifles carried by other members of the unit; this reduces logistical requirements by making it only necessary to supply one type of ammunition to a unit. Squad automatic weapons are light enough to be operated by one person, as opposed to heavy machine guns such as the M2 Browning, which fire more powerful cartridges but require a crew to operate at full effectiveness. One of the first weapons used in this role was the Madsen machine gun. Although limited in today's terms, the Madsen was introduced in an era when the standard infantry rifle was a bolt-action repeater with fixed magazines reloaded with single rounds or chargers; the Madsen was capable of automatic fire. Though over 100 years old, the Madsen is still in limited use today; the standard machine guns of this era were of the Maxim type.
Used by the British and the Russians, these weapons were bulky, tripod-based, water-cooled, they required a team of four men and, although excellent in the defence, were not suited to manoeuvre warfare. Another pioneering weapon in this role was the Browning Automatic Rifle. Introduced late in World War I, it remained in front-line service into the Vietnam War. Intended as an automatic rifle capable of delivering suppressing "walking fire" in the advance, the BAR came to be used in the light machine gun role. During World War II, as the importance of having a source of mobile automatic fire increased, the number of BARs in a unit increased, until in some units it represented 1 in 4 of the weapons present in a squad. During its long service in the US military, it was pivotal in the evolution of U. S. fireteam tactics and doctrine. Modern squad automatic weapons are modified assault rifles or battle rifles that may have increased ammunition capacity and heavier barrels to withstand continued fire and will always have a bipod.
In the case of some assault rifles, such as the H&K G36 or Steyr AUG, the SAW is the standard rifle with a few parts replaced. However, the Austrian Army, though issuing the Steyr AUG rifle, does not issue the HBAR variant. Instead, the 7.62mm caliber MG74, a derivative of WW2-era German MG 42, is issued. Light machine guns, either belt-fed or magazine-fed, may be used as squad automatic weapons, as may be general-purpose machine guns; the most common squad automatic weapons in use today are derived from two basic patterns: the Kalashnikov-based RPK or the purpose-designed FN Minimi. FN Minimi FN SCAR L86 LSW L110A1 FN Minimi Beretta AS70/90 West Germany's original plan in the late 1980s was to adopt the new 5.56mm Heckler & Koch G41 assault rifle to replace the 7.62mm Heckler & Koch G3 battle rifle and the 4.7mm Heckler & Koch G11 carbine to replace the 9mm IMI MP2 Uzi and Heckler & Koch MP5. The end of the Cold War and the reunification of Germany in 1990 forced everyone to scramble for a cheap alternative.
The G36 family was created from a proof-of-concept prototype rechambered to fire the 5.56mm NATO cartridge. It is composed of an assault rifle, light machine gun, assault carbine, assault submachine gun. Heckler & Koch G36 HK416 HK417 The Italian military flirted in the 1980s with the idea of adopting a heavy-barrelled magazine-fed 5.56mm automatic rifle. It was to accompany the companion 5.56mm Beretta AR70/90 assault rifle and supplement the 7.62mm MG 42/59 general purpose machine gun. A rethinking of the concept led to their adoption of the belt-fed FN Minimi instead; the Netherlands Marine Corps is the only part of the Dutch military to use the LOAWNLD as their squad automatic weapon. All other branches use the FN Minimi for this role; the Russian support weapon concept was designed around providing one standard cartridge that could be used by the clip-fed rifle, magazine-fed assault rifle and belt-fed light machine gun. The SKS and RPD were dropped as being less effective; the RPK, with its magazine and parts commonality with the base AK-47, was more effective.
It replaced the RPD as soon. RPK RPKS RPK-74 RPK-74M/RPK-201/RPK-203 RPK-16: The RPK-16 squad automatic weapon is a new light support weapon, expected to take over the role of its predecessor, the RPK-74, in the Russian Armed Forces. In United States usage, the M249 light machine gun is referred to as the Squad Automatic Weapon. In the 1970s the United States began realizing that they might have to fight a conflict in the deserts and mountains of the Middle East or Near East rather than the jungles of Asia or forests of Europe and Eurasia; the Squad Automatic Weapon program was designed to create an intermediate weapon between the M16 rifle and M60 machine gun. It would have to fire tracer ammunition out to a visible range of 800 meters or more, be capable of accurate high-volume sustained fire
A handguard on firearms is a guard attached to the front of a firearm to grip the weapon from the front. It allows the user protection from the barrel, which may become hot when firing, it gives room for more attachments to the weapon itself, such as an M203 grenade launcher. A handguard is a part of a sword or knife, just above the handle, it protects the wielder's hands from an opponent's blade. Barrel shroud Finned carbine handguard assembly Randy E. Luth
The SA80 is a British family of 5.56×45mm NATO small arms, all of which are selective fire, gas-operated assault rifles. The L85 Rifle variant has been the standard issue service rifle of the British Armed Forces since 1987, replacing the L1A1 variant of the FN FAL; the first prototypes were created in 1976, with production of the A1 variant starting in 1985 and ending in 1994. The A2 variant came to be as the result of a significant upgrade in the early 2000s by Heckler & Koch and remains in service as of 2018; the A3 variant was first issued in 2018 with several new improvements. The remainder of the SA80 family comprises the L86 Light Support Weapon, the short-barrelled L22 Carbine and the L98 Cadet rifle; the SA80 was the last in a long line of British weapons to come from the Royal Small Arms Factory, the national arms development and production facility at Enfield Lock. The idea dates back to the late 1940s, when an ambitious programme to develop a new cartridge and new class of rifle was launched in the United Kingdom based on combat experience drawn from World War II.
Two 7mm prototypes were built in a bullpup configuration, designated the EM-1 and EM-2. When NATO adopted the 7.62×51mm NATO rifle cartridge as the standard calibre for its service rifles, further development of these rifles was discontinued. In 1969, the Enfield factory began work on a brand new family of weapons, chambered in a newly designed British 4.85×49mm intermediate cartridge. While the experimental weapon family was different from the EM-2 in internal design and construction methods, its bullpup configuration with an optical sight was a clear influence on the design of what was to become the SA80; the system was to be composed of two weapons: the XL64E5 rifle and a light support weapon known as the XL65E4 light machine gun. The sheet metal construction, the design of the bolt, bolt carrier, guide rods, gas system and the weapon's disassembly showed strong similarities to the Armalite AR-18, manufactured under licence from 1975 to 1983 by the Sterling Armaments Company of Dagenham and, tested by the UK MoD in 1966 and 1969.
During the development of the SA80, a bullpup conversion was made of an AR-18 and a Stoner 63 at Enfield due to the fact they could be used with stocks folded/without stocks which allowed the bullpup conversion and were chambered in the experimental 4.85x49mm round. A bullpup conversion of the AR-15 was considered but the buffer tube in stock prevented the idea. Technically, in the mid-1970s, the 4.85×49mm round was seen as superior to the existing version of 5.56mm M193 round in use by the US and by other forces. It should be noted that development of small-arms munitions have a long and continuous life and it was estimated by the trials specialists from Enfield that this weapon would be superior in the 4.85mm configuration. For the 4.85 mm round, both propellant and projectile were at the beginning of their respective development curves. Weight for weight, more rounds of ammunition could be carried by an individual soldier – a considerable advantage on the battlefield, it was regarded as probable at the time that the argument for the 5.56 mm standard within NATO had more to do with the economics involved.
Over the lifetime of a small-arms weapon type, far more money is spent on the munitions than the weapons themselves. If the 5.56 mm supporters had lost the argument in favour of a British 4.85 mm round, the economic impact would have been large and political pressure undoubtedly played a part in the final decision. In 1976, the prototypes were ready to undergo trials. However, after NATO's decision to standardise ammunition among its members, Enfield engineers re-chambered the rifles to the American 5.56×45mm NATO M193 cartridge. The newly redesigned 5.56 mm version of the XL64E5 became known as the XL70E3. The left-handed XL68 was re-chambered in 5.56×45mm as the XL78. The 5.56mm light support weapon variant, the XL73E3, developed from the XL65E4, was noted for the full-length receiver extension with the bipod under the muzzle now indicative of the type. Further development out of the initial so-called "Phase A" pre-production series led to the XL85 and XL86. While the XL85E1 and XL86E1 were adopted as the L85 and L86 a number of additional test models were produced.
The XL85E2 and XL86E2 were designed to an alternate build standard with 12 components different from E1 variants, including parts of the gas system and magazine catch. Three series of variants were created for "Environmental User Trials". XL85E3 and XL86E3 variants were developed with 24 modified parts, most notably a plastic safety plunger; the E4's had 21 modified parts, no modification to the pistol grip, an aluminium safety plunger, unlike the E3 variants. Lastly, the E5 variants had 9 modified parts in addition to those from the E3/E4 variants. SA80 development was complicated from the start. One complication was at least three project staffing changes at the Royal Small Arms Factory, which resulted in repetition of testing several times. One problem with the design of the gun itself was that the cases would be ejected at varying angles as it heated up and the rate of fire changed, resulting in a large ejection port; the conversion from 4.85 mm to 5.56 mm caused a complication, as the rate of fire dropped as the gas port was left in the same position, but the pressure and time curve of the rounds w