I have not done any carving on grips/gunstocks that are already made. I would scan or find the files for the pistol grips and carve new ones, much easier and if you mess up on the other ones you are going to be doing it anyway.
I think Berg came up with something to do it, I was too skeert to try!!!! I didn't want to buy $250 plus gunstock.
Brent
A,B machines, PE,probe,conforming vectors, centerline, 2d,3d,stl and dfx imprt, rotary , 3.xx, Pattern Sculptor
OS X Yosemite
Woodwork is what I do to pay for my tool addiction.