[HighValleyRanch]

RodFac, thanks for asking.
On the freehand routing, I use a clear base on the router so I can see better. I use a 1/4" straight double fluted bit.
I take out the locator pin on the frame so that I can best lay it flat and trace the best out line of the frame. You can't get it exact, but close enough. I include the upper part which has to be insetted deeper.
I do three cuts to get to the right depth. ONLY take I/3 or less of the router diameter cut. That is the key to keep it from wandering. I just route the entire cutout. On the third cut, I set the exact depth by using a grip that has already been insetted, either my own, or one that has been cnc cut to the right depth.
Once I can get the frame fitted into the routed cutout, then I trace the upper part of the frame including the half circle key. I take two cuts to get the right depth using the model grips for correct depth.

FWIW, I have been a well knowncustom grip maker for over thirty year making anatomical grips for the Bullseye community. I was most likely the only one doing everything by had. For most of the guns, I made jigs that I would inlet with a router setup that was made for cutting dovetail joints. But for most of the revolvers and custom guns, I did the routing by hand.
I retired two years ago from my grip business, and so doing these grips brought back a lot of memories.