The only thing I am not a fan of in regards to the AR39 is the weaker bolt face. Its one of the reasons I got the mutant. Its a shortened AR 10 receiver and carrier with a full sized 308 bolt. No worries about the lugs failing from hard/fun use.No doubt it is, I am a 7.62x39 AR fan and use it for both those purposes as well. Maybe that is part of why the 300BLK never really got me.
Otherwise the feeding issues seem to have been worked out with newer magazines. I like that the mutant takes AK magazines too.
Also, 762x39 is still far cheaper than 300 bo