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.

Voting for anti-gun Democrats is dumber than giving treats to a dog that shits on a Persian Rug