Cutting the stock @ 90 degrees to rib line will leave you with 0 pitch.
I agree with those that reccomend cutting in smaller increments to arrive at the proper length. If you make your cut parallel to the end of the butt will maintain your present pitch. Only you know whether that is a good or bad thing. If it's not good you can adjust with your incremental cuts.
When you make the cuts, make sure the butt of the stock is perfectly perpendicular to the surface your stock is resting on, otherwise the cut will be made at an angle to the butt instead of square with it. If I have told you something you already know I apologize for being redundant.
Hack
