"Magazine" and "clip" have become synonymous. A "clip" is not exclusive to an in-the-grip interpretation, though Kel-Tec, and perhaps others, make a pistol with a 30-round in-the-grip "clip," though Kel-Tec, itself, calls it a "magazine."  "Clip" is also often used to refer to 30+-round "banana" magazines, where the upper portion slides into a rigid sheath below the receiver which also serves as a forward grip on military-style semi-automatic rifles. Your criticism of Shannon's syntax is without merit.