Excellent question Kevin.
With the barrel against the door jam, and the heel on the floor, measure the distance of the toe off the floor. that is what I was referring to as pitch. This is a more useful dimension that putting the butt flat on the floor and measuring the distance the muzzle is from the wall, because of the variability of barrel length.
The angle of the butt is profound when shooting the piece. Take a Tulle trade gun for a vivid example. These guns: the reproductions at least, have an exaggerated pitch - the toe is a long distance off the floor. The consequence of this is that when you fire the gun, the stock slides under recoil upwards on your shoulder, and the comb slaps your cheek bone. All other architecture of the butt seems to be fine - drop at comb, length of pull, etc, yet the guns are not shooter friendly.
Now take a Long Land Pattern of the King's Musquet: the 1st model Brown Bess. This smoothbore has a pitch that keeps the butt against the shoulder upon firing it, and even with dimensions similar to the Tulle in terms of drop at comb and length of pull, the musket doesnot slap you in the cheek bone, in spite of a much heavier ball and more propellant. The same cannot be said for 2nd and third model Besses which have similar pitches but higher combs - they were not meant to be aimed at the target, but I digress.
My brother Daryl has a 20 gauge smoothbore of English design whose pitch is if anything, not sufficient. That is the toe contacts the floor first rather than the heel. But it is possible to shoot this gun with huge charges of powder without bruising your cheek, because the opposite effect happens: the butt slides down and away from your face upon firing the gun. This phenomenon is hardly noticeable in practice, yet the effect is profound.
Hope this helps clarify.
