300 BO is more expensive to run and even the supersonic loads aren't quite as hot as 7.62x39. Close in some cases, but 7.62 commie is a tad more powerful. 300 BO, however, has many other bullet options that improve it's performance for both sub and supersonic. What I don't like about 7.62x39 is that it's almost always corrosive. Hopefully PSA's version will include brass cased boxer primed ammo in addition to steel cased. In any event hopefully all will be non corrosive.
Another take on AK vs AR by the MAC that goes into further detail and addresses the myths surrounding relative reliability.
