Has to do with ballistics I believe. It was in reference to a 6.5-06 AI. The 120s are little lazers, but at about 400 yards or so, the 140s become the lazers with added pop.
If you got the time/money, try Wildcats; you can get his RBBT match style bullets or bonded FB bullets (LD profile) in 5 gr increments from 120-140 and some real heavy-weights. Richard is getting some new dies that will produce bullets with the max attainable bc per die maker.
Give Richard a call or shoot him an email. He can answer any question you have about it.