The Zastava M21 is the service rifle of the Serbian armed forces and it gets the scrutiny of The Firearm Blog in this video... "In this episode of TFBTV, James Reeves is at Zastava Oruzje in Serbia to try out a number of their most famous (and infamous) small arms. In today’s video, James has the opportunity to shoot the M21. The Zastava M21 is similar to the Zastava M90 but it has a few changes making it something slightly different. However, it might be the lightest recoiling 5.56mm rifle made. James interviews a Zastava engineer to get the details on how the Zastava M21 works the way it does."