It seems that the terms Prince of Wales grip, half pistol grip, and semi-pistol grip are pretty much interchangeable. I don't believe that guns with true Prince of Wales grips are ever capped, but there are some half pistol grip guns which have a rounded cap that follows the same shape as an uncapped half pistol grip. I don't see the term knob grip used very often, and it seems to be used more to describe grips which are more bulbous.

Originally Posted by Geoff Roznak
The NRA has proven itself unreliable and corrupt. Period.