Why does an FCC metal generally show higher ductility than a BCC metal with a similar atomic packing factor under comparable conditions?

Ductility is the ability of a material to deform plastically, or change shape permanently, under tensile stress before fracturing. This plastic deformation in metals primarily occurs through a process called slip, which involves the movement of line defects known as dislocations. Dislocations are extra half-planes of atoms that move through the crystal lattice, causing atomic planes to slide relative to each other. For slip to occur, dislocations move along specific crystallographic planes, called slip planes, in specific crystallographic directions, called slip directions. A combination of a slip plane and a slip direction constitutes a slip system. The ease with which a metal deforms plastically is directly related to the number and nature of these available slip systems; more easily activated slip systems allow for greater shape change and accommodate varying stress orientations, leading to higher ductility.