BattlerifleG3 - If I remember correctly, the Norinco SKS-D was shortened, to make it a "Paratrooper" rifle/carbine.
I can't understand why everybody wants to go to a shorter and shorter barrel, and try to shoot 500 yards. Is it the added challenge??? The short barrels reduce the accuracy, two ways, they shorten the sight radius, and they shorten the guidance of the barrel, additionally half the power from the powder is blown out the muzzel of the barrel, creating a louder bang (maybe more bang for the buck?). Long distance shooters, even with the AR-15 use barrels up to 26 or 28 inches at least. The guys with the "Quigley Down Under Rifles" (.45-110, .45-120, and the .50-90, and on and on) go out even further and those can be accurate out to and beyond 1,200 yards (the bullets have been proved recently to be able to go out 3,600 yards at Yuma proving ground).
Can anybody give a rational explanation for the trend to short, short barrels?