Select fire means you have a choice between semi-automatic and fully automatic. The M-16 had a version that used 3 round burst but it had problems in service. And you’re simply mistaken about the recoil of the 7.62 NATO round. It’s a full power rifle road capable of killing 1,000 yards away. It’s recoil is several times that of the 5.56 round in the M-4/16, especially since the rifle in question only weighs 7 lbs. Actual experience in service has proven what I’ve said to be true. Are you familiar with the BAR rifle developed by John Browning? We used it as a squad machine gun in WWII and later. It used the 30–06 round that was replaced by the 7.62 NATO, virtually identical ballistics in Army service. It weighed between 16–20 lbs depending on version. That’s the kind of weight you need to be able to fire such a powerful round for even a burst of automatic fire.