I see the attraction of the 6.5mm round's introduction as a general purpose rifle munition, as it's a midpoint between 5.56 and 7.62- however 7.62x51 was proven to be a terrible general purpose round in the Vietnam war- the US M14 was uncontrollable when firing in bursts, and a soldier's ammunition capacity was much lower because the rounds were heavy and magazines could only hold 20 rounds.