The "flat side" rounded frames that were ordered back before the Custom Shop took over production had the side panels and bottom edges removed by hand file. This left a slight bulge on the sides of the frame, only noticed on close inspection. A picture on page 52 of Schwing. The weight saving was less than 2 oz.
The Custom Shop guns had the side panels milled off for a flat side rounded frame(the bottom edges of the frame and the area behind the fences were rounded).
Now, in the first year of production, there were a few "true" flat side frames built. They had no side panels and had sharp edges at the bottom of the frame except for a small are at the hinge pin that was rounded. Picture on page 51 of Schwing.
I agree with Larry, I like the side panels much better that the smooth sides.
