I don't know how they produced PC stocks, but they obviously did more than just round off the bottom.
Here's a photo of the bottom of the N diamond PC's I sold:
I don't have N Magna's to compare, but I do have both styles of K frame. The bottom of the checkering is substantially higher up, but they routed a much wider border at the bottom. It appears that bottom was rounded before the stocks were checkered, since the area below the border of the PC's is higher than the bottom of the checkering on the standard Magna's.
