I think the 300 BLK (and the newer 30 HAM'R) are the best of both worlds: The thump of the 7.62x39 .30 caliber, with the accuracy and modular capability of the AR platform, and uses the common 5.56 magazines. I tried a 7.62x39 AR, but it was a flop, and there were no reliable mags to be had.