The GC would seem to grip the rifling better?
Between the gc and bottom drive band together they make a long bottom drive band compared to the keith 429421. And the gc does what it's supposed to do, seal the bbl which leads to accuracy.
Other then that the h&g #142 and the lyman 429421 are pretty much the same. Same oal, same amount of bullet get seated in the case same surface area with the #142 gc and 3 drive bands vs the 429421 3 drive bands.