It was announced in October 1983, FN were seeking to develop a more powerful replacement for the .50" Browning, better able to penetrate light armoured vehicles (in effect, a Western equivalent to the Soviet 14.5mm KPV heavy machine gun. FN initially selected the 20mm Hispano case as a basis and necked it down to 15mm for the FN-BRG (15x115). The weapon and its ammunition had a protracted development and finally emerged as a 15.5mm because of fast barrel wear.
The 15.5x106 was FN's second effort to make a KPV competitor in the BRG-15, appropriately by necking out the KPV's case. It also utilized an unusual dual feed device (A la Hafdasa C-4), with link ammunition belts feeding from both the right and left. Spent shell casings were ejected out of the bottom of the gun, as in FN's later P90 personal defense weapon. The quick-change barrel assembly developed for the BRG-15 was redesigned for use in an updated version of the M2HB.