All I can say is that these are state of the art weapons systems, it is capable of engaging targets up to 2000 meters (that is if the operator is competent to make the shot). The rifle can fold in half (down to about the size of a Dragunov SVD), it is semi automatic and the magazines holds 5 rounds. It shares the same ammo as the DShK heavy machine gun. Logistically they should have no problem obtaining ammunition for it if they can secure DShKs in their inventory.
I am unsure how the the FSA got ahold of these, but this is quite a specialized tool. Essentially it is a .50 caliber sniper rifle in Western terms (Barrett Light Fifty weapon systems). There has been reports of the rifle taking out grounded aircraft and light armored vehicles.
FSA fighters showing off their OSV-96s, it comes complete with the factory issued PKN-05 Night Vision optical sight.