If I am not badly mistaken, which I might well be, which set 1200 fps for a 3-1 1/8 load was measured at 15 feet, thus is not true muzzle velocity. As soon as the charge has opened where individual pellet drag begins to take affect initial velocity loss is quite high. This occurs well before reaching 15 feet. Thus the 3 1 1/8 load's actual MV was somewhat higher than the reported 1200 fps.
In many ways the older method of measuring the velocity over 20 or 40 yards was more meaningful than muzzle velocity. Two things it shows is the higher retained velocity of larger shot as ShtGnJones mentioned. It also shows that the 18% velocity increase going from 1100 to 1300 fps does not give anywhere near an 18% increase "Down Range" where the actual contact with game is made. Little round pellets are very inefficient above Mach 1 (speed of sound).
