to my knowledge Zastava started chrome lining barrels only in the 80's probably with obtained technology from M84 Škorpion or M84 General-Purpose Machine Gun (licenses for both were purchased in conjunction with M84 Main Battle Tank)
M70, M72, M76, M77, M91 and M92 did not have chrome lined barrels (even today)
while Zastavas 5.56 Series (M80, M85, M95, M21...) and M84 as well as CZ 99 Series have chrome lined barrels
Also Zastava used high polish method in their non chrome lined barrels to give them a level corrosion resistance (method of polishing inside of the barrel preventing corrosion from forming) high polish is as good as chrome lining but it is also more expensive and time consuming