In the mid-1970s, the Swedish Armed Forces decided to follow the general transition towards smaller calibre ammunition and directed the FMV (Defence Materiel Administration) to procure a suitable replacement for the Ak 4 capable of using 5.56×45mm NATO ammunition, which under STANAG 4172 is a standard cartridge for NATO forces as well as many non-NATO countries. The weapon was required to be highly reliable in the near-arctic climate of northernmost Sweden, as well as being easy to handle and maintain, while meeting a certain minimum level of accuracy.
After evaluating and testing eleven different 5.56×45mm NATO assault rifles from 1979 to 1985, the FMV chose the Belgian FN FNC, which received several modifications. These included a larger trigger guard and cocking handle (to allow for operation while wearing winter gloves, a necessity for temperatures reaching down to -30 °C (-22 °F)), a larger handguard, a different collapsible shoulder stock, different iron sights and gas block, a modified bolt, deletion of the 3-round burst capability, and a corrosion-resistant green (instead of black) finish. Further the detachable box magazines were modified to be interchangeable with the M16 rifle STANAG magazines. Swedish blank ammunition uses a wooden plug in place of a bullet, so the flash suppressor was fitted with grooves to accept the Swedish blank-firing adaptor, which prevents potentially dangerous pieces of wood from leaving the weapon by smashing the plug into a fine sawdust. The flash suppressor was also designed to accept rifle grenades, although none have been accepted into service.
During the troop trials there were an alarming number of complaints by soldiers about damaged teeth from being struck in the mouth by the blank firing adaptor. This was revealed to be caused by the practice of having the weapon slung across the chest rather than the back. Rather than changing this practice (which would reduce the ability of the soldier to rapidly bring the rifle into action), a special plastic cap (later changed to a hard rubber version) was issued to cover the adaptor.