Rabbit, Roland is still around. He lives, or at least visits often, on the trapshooters web site BB. I have his booklet and there is some good information. Not the definitive source on fit but some good information.
As to pitch and my experience, it is similar to what bad ol' craig does. I shoot alot. Probably average 3 flats a week at sporting clays, bunker and some American trap and skeet. I own several guns. Though I primarily shoot one I do fiddle around with stocks and other guns quite a bit. I have found that the right amount of pitch is EXTREMELY important in taming recoil, especially face slap. This issue of the gun "slipping off the shoulder" is not something I am aware of. However, the gun coming up cleanly to a good position is an issue. That is kind of a combination of LOP and pitch. When that works, then if the gun slaps the face for my usually a bit more pitch is in order.
I just take off the butt pad or plate and put in some hard cardboard spacers top or bottom (for me usually top to increase pitch) till it is right. I check if it is right by shooting a round or two. Nothing real scientific. But the results are dramatic. When it is right, the gun does not noticably jump. Anyway, for what its worth.
Regards, Jake
