 The rifle is in service with the Serbian army, where it replaced the M76, which was chambered for the 7.92×57mm cartridge.Zastava's website claims that the M91 rifle was designed after a long and careful study of combat tactics and experience of military and police special forces worldwide; and that its development has been carried out under supervision and in close cooperation with some of the most experienced and capable special and anti-terrorist units.Current modernisation of Serbian forces is proceeding on the basis of a plan designed during the late 1990s known as Model-21.