STOCK GEOMETRY
There is nothing like a good problem to keep one inside and busy on a sub zero day. I think I have figured out the geometry of pitch. A diagram and explanation are attached.
The pitch table indicates that 3.5 +/- 1inch is the common value for Parker field gun pitch as measured by the wall method. I made up a geometric diagram based on common Parker dimensions; 30 inch barrel;14 1/4 inch pull;2 3/4 inch drop at heel(dah); 1 5/8 inch drop at comb(dac) ; and 3.5 inch pitch. I measured several 12ga Parkers and found the arc of the trigger to be 2 inches behind the breech, and the comb to be 7 inches behind the breech.
This diagram determined that the Parker heading up and butt plate tooling for machine inletting and carving stocks was set up to cut the butt at an angle of 1 : 8 relative to the breech. That is 7.2 degrees relative to the breech face, and 82.8 degrees relative to the rib. That cut provides 3.5 inches of pitch for the standard dimensions noted above.
Changes in dah cause a 1 inch change in pitch for each 1/2 inch change in dah. Changes in barrel length cause a 1/8 inch change in pitch for each inch change in barrel length. Changes in pull change pitch 1/16 inch per inch change in stock length. All of these changes in wall pitch occur with constant pitch angle at the butt; ie they produce no change in "feel".
Pitch as such does not influence recoil against the face; this is the result of slope of the comb due to difference dac - dah. A monte carlo can provide dac - dah = 0 for no face recoil, while keeping a lower dah for faster mounting.
Best, Austin
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