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.

[6] 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.

This was the expressed view of trials team members whilst demonstrating the XL64E5 prototype at the British Army School of Infantry at Warminster.

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 ultimately be superior in the 4.85mm configuration.

If the 5.56mm supporters had lost the argument in favour of a British 4.85mm round, the economic impact would have been very large, and political pressure undoubtedly played a part in the final decision.

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.

The XL85E2 and XL86E2 were designed to an alternate build standard with 12 components different from E1 variants, including parts of the gas system, bolt, and magazine catch.

[16] After receiving feedback from users and incorporating the various design changes requested, including adapting the rifle for use with the heavier Belgian SS109 version of the 5.56×45mm round and improving reliability, the weapon system was accepted into service with the British Armed Forces in 1985 as the SA80.

Upgrade programmes and requirements for spare and replacement parts have since been fulfilled by then British-owned Heckler & Koch, which later reopened the Nottingham site.

The Bermuda Regiment adopted the Ruger Mini-14 in 1983, although small stocks of the L85 were also acquired for the purpose of familiarisation training as many of its personnel attend courses or attachments in Britain.

Components were found to be insufficiently robust, the LSW's bipod lock often failed to hold the bipod legs in closed position, the plastic furniture was melted by insect repellent, metal parts were quick to rust in jungle environments, and the weapon's mechanism was highly susceptible to dusty and arctic environments.

[citation needed] There were also issues with regard to working practices and employee attitudes at the Enfield site which were exacerbated by its closure in 1988 and resulting redundancies.

[29] The SA80 initially gained a poor reputation amongst British soldiers as being unreliable and fragile, a fact picked up by the UK media,[30] entertainment industry,[31] and members of the House of Lords.

[32] Special Air Service sergeant Chris Ryan regarded the SA80s as being "poor-quality, unreliable weapons at the best of times, prone to stoppages, and it seemed pretty tough to have to rely on them".

Some platoon commanders considered that casualties would have occurred due to weapon stoppages if the enemy had put up any resistance in the trench and bunker clearing operations.

[16] The modified A2 variants are distinguished by the "HK A2" marking on the top of the weapon just forward of the buttplate and the distinctive comma-shaped cocking handle (shaped to aid the ejection of the empty round casing and prevent stoppages).

[16] A further upgrade including the provision of Advanced Combat Optical Gunsights (ACOGs), a Daniel Defense-designed Picatinny rail (RIS) handguard for the L85 rifle (with optional Grip Pod downgrip),[40] and a new vortex style flash eliminator was introduced as an Urgent Operational Requirement; initially introduced for use by selected units in 2007,[41] the upgrade package was subsequently rolled out on a more general basis from 2009 onwards.

[45] The changes from the SA80A2 design include a modification to the upper receiver and a full-length rail system for optional add-ons such as a vertical foregrip, laser pointer and torch.

These upgrades mainly included improvements to the ergonomics of the handguard and a switch from Heckler & Koch's HKey accessory attachment system to Magpul's M-LOK.

[50] With the exception of the L98A2, the SA80 system is a selective fire gas-operated design that uses ignited powder gases bled through a port in the barrel to provide the weapon's automation.

Mounted on the SUSAT's one-piece, pressure die-cast aluminium body are a set of back-up iron sights that consist of a front blade and small rear aperture.

Rifles used with other branches of the armed forces when not on operations are configured with fixed iron sights, consisting of a flip rear aperture housed inside the carrying handle and a forward post vertical blade foresight, installed on a bracket above the gas block.

[17][page needed] In 2011, the Ministry of Defence began issuing ELCAN SpecterOS 4× Lightweight Day Sights (LDS) in an effort to replace ageing SUSAT units across the British Armed Forces, forming the first stage of the FIST infantry enhancement project.

[58] The Beta C-Mag was trialled in an attempt to improve the L86's limited ability to lay down sustained fire, but reliability problems with the magazine when loaded with British-issue ammunition meant that it was not adopted.

On operations with ground close combat units (Infantry, Royal Marines, RAF Regiment), the rifle is often fitted with an LLM01 Laser Light Module and deployable bipod mounted within an optional front grip.

Various underbarrel grenade launcher models were trialled, including the M203 and a proprietary "Enfield Close Assault Weapon" developed by Royal Ordnance.

The weapon has a heavier, longer 646 millimetres (25.4 in) barrel than the rifle and features a shorter handguard with an integrated bipod protruding from the front.

[citation needed] The LSW has the additional issue of its inability to deliver sustained automatic fire as it lacks a belt feed.

The role of a LSW was ultimately filled by the FN Minimi, known in service as the L110A1-A3 light machine gun, a belt fed weapon with a quick-change barrel in the same way as the GPMG.

The barrel terminated immediately in front of the pistol grip, which in combination with the lack of any sort of foregrip or handguard presented a risk of self-inflicted gunshot injuries if the firer's left hand was to slip forward.