The two top guns are 10ozs apart in weight. The M4A2 has a heavier A2 upper and 4-pos stock (the plastic part is heavier). Both the upper and the stock contribute to the 10ozs along with the additional meat on the M4 bbl.
I would estimate about a 6oz difference in weight between a stripped 16" M4 and a stripped 16" pencil bbl. Maybe an additional ounce or two off that for a 14.5 M4.