My 20ga stock cut perfectly flat, but I had to slightly sand my 12's stock after cutting to get it flat.
In order to keep the factory pitch, I placed the end of the stock against the blade before cutting, and then matched the angle on my miter gauge, it was a 7 degree setting. Still, I think I ended up with more pitch than before, as I see a little more of the rib than I used to, but since I installed, "higher", than factory sight beads, I think it balanced out as they both hit well when I shoot them.
Also, make sure when you lay your stock down that it's square to the table. You may have to shim it, or, tilt the blade to match the angle. Thankfully, both my stocks laid flat.
I made a sacrificial, (crosscut sled), using a thin sheet of wood under the stock to protect it from dragging across the table, and a backer board attached to my miter gauge to reduce tearout from the cut. Also, be sure to wrap your stock with tape to reduce the possibility of tearout from the cross grain cut.
Drill the pad holes after cutting. Center your pad, mark and drill one of the holes, put in a screw, then mark and drill the 2nd hole.
The pads will overhang quite a bit before sanding them down.
Take a scribe, and mark the base of your pad all the way around the contour of the stock so you have a line to follow when removing the bulk of the overhang. I don't have any photo's yet of the sanding operation as I have only sanded my 20ga pad, and still need to do the 12. Here is the finished 20ga pad.
When you get close, install the pad and keep a couple of layers of tape on the stock, and sand the pad while on the stock to get the heel and toe, (top & bottom edges), of the stock's angle's correct. When you get close enough to start contacting the tape, (be VERY CAREFUL here so you don't go through the layers of tape and gouge the stock with the sander), stop, remove the pad, and finish it out by hand with 320 grit sandpaper and a light application of oil. I did it this way because I do not have a pad sanding jig.
Take care and let us know how it turns out

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