The main thing is that they switched from the non-rotating claw extractor controlled round feed to a push feed design. They made some other cosmetic changes which were poorly executed, like free floating the barrel and leaving an excessive gap around the inletting. Overall they made it cheaper and what they did to make it cheaper was not well received by a basically conservative (in taste) clientele.

Gunnery, gunnery, gunnery.
Hit the target, all else is twaddle!