Geo, and others.......this is what Michael Yardley wrote. I consider him one of the premier writers in explaining gunfitting.
"We have not yet said much about pitch (sometimes called 'stand'). The length of the stock from the middle of the trigger to the heel and the toe control the pitch of a gun and, when taken together with the length of pull, the shape of the butt sole too. Pitch concerns the angle of the of the butt sole relative to the axis of the rib and may be measured approximately by standing the gun against a wall, with the top of the action touching it's surface and the butt sole against the floor (make sure that the wall is truly perpendicular to the floor). If you are really keen, pitch can be measured in degrees in a specialist jig (measuring in this fashion is more precise because barrel length does not affect the result). Typically, the measurement is about 2" 'pitch down' on a sporting clays or skeet gun, but may be significantly less on a dedicated trap gun (which, of course, is intended exclusively for rising targets). Some trap guns may even have positive pitch). The pitch measurement is also important on a hunting gun. In live quarry shooting, there is a need to keep well up on line as the swing progresses. The right pitch dimension will facilitate this and makes rising and crossing shots in the field significantly easier.
Rather than encouraging you to get protractors out, I would say that the simple rule for pitch is to create a stock in which the surface of the butt sole is in comfortable full-length contact with the shoulder when the gun is mounted and in which there is no unwanted tendency for the barrel to point up or down relative the line of sight. If the toe or heel of the butt sole or its centre are not in firm contact with the shoulder, or, if the pitch measurements cause the butt sole to catch or slip at the shoulder something is clearly wrong. When the gun is mounted, watch to see if the heel or toe are coming to the shoulder first. Temporary adjustments to pitch can easily be made to guns with butt plates or recoil-pads by loosening off the screws and introducing shims. Women and men with large chests may want a reduced toe measurement and, often, a rounded toe as well.
One of my approximate tests for pitch involves asking the client to point a proven empty gun at my eye from a range of about 15 feet [this is not something I do lightly or without stringent safety procedure]. As a starting point for experiment, what I want to see is the striker/firing pin hole well centred in the circle of the muzzles as I look down them (which is indicative that the gun is not tipping up or down relative to the line of sight). In case you think that this sounds rather difficult, I might add that, provided you are standing with some light behind you, it is usually surprisingly easy to see the breechface and striker hole from the muzzle end of the gun - even if you are some distance away."
I found this to be particularly clear............SRH
