The M91 is a semi-automatic, air-cooled, detachable 10-box magazine-fed firearm with a fixed stock. In concept, it is similar to the Russian Dragunov SVD sniper/designated marksman rifle. While the design of the M91 is based upon an elongated version of the Avtomat Kalashnikov 1947 AK-47 design just like its predecessor, the Zastava M76, the rifle features several modifications, bringing it closer to its Soviet counterpart, the Dragunov sniper rifle. The separate stock and pistol grip used on the M76 have been replaced with a thumbhole combination stock made of synthetic polymer material resembling that used on the Russian Dragunov SVD rifle. The chambering is the Russian 7.62x54mmR cartridge which is the same used in the Dragunov SVD. It is suited for long-range use, and replaced the 8x57mm IS round in Serbian service. Overall, the design of the flash suppressor, the magazine used, the simplified PSO-type rangefinder reticle used in earlier Zrak telescopic sights, even the distinctive shape of the pistol grip and modified bolt carrier (as well as a milled receiver) - all these attributes strongly point at SVD as the design's template.
A side-rail on the left wall of the receiver accepts various telescopic sights and night optics. The standard daylight telescopic sight for the M91 is the ON-M91 6 x 42. For low light conditions the rifle can also be equipped with PN 5 x 80 passive sights of the first and second generation of Night vision devices. The optical sight can be removed from the rail and reinstalled without loss of zero.
The rifle features adjustable backup iron sights with a sliding tangent rear sight which can be adjusted from 100 m to a 1,000 m. These can be employed if the primary optical sight is damaged.
The best results are obtained at ranges up to 800 m. The maximum aiming distance offered by the optical sight and iron sights is 1000 m. For targets of height of 30 cm (head silhouette), the effective range is approximately 320 m, for chest silhouette (height 50 cm) the range is 450 m and for a moving silhouette (150 cm) the effective range is 650 m.