Ken, explained that to me just today, here is what he wrote
"If your BATAC has the Black/Tan G-10 handles, then they are Magnum handles. For the BATAC, or any knife that uses the TAC handles, Magnum simply means that the handles are thicker. But, for the larger knives, Magnum means more contouring. The thickness between the tube fasteners is narrow, and wider at them."