Let's get our feet back on the ground here chaps........ In the real world of Armourers shops, we stoned the sear surfaces of these things all day, every day to set the pull-off weights and when setting up bolts. So long as you remember to keep the surface square and at the correct angle as stated by Bruce and are careful/workman-like you don't need to worry too much about failures. Just remember that you can deviate from the 'angle of attack' or the angular relationship between the sear and face of the C-P.....but.....! Any deviation will affect the pull-off weight to a greater extent than you thought possible.
Stoning C-P's was always by hand using the 'Stones, Armourers, tri-corner, flat. VAOS number B2/5345-99-961-7763. UP and DOWN and NOT across don't forget. No need for anything fancy in my world