blackjack,
i'm fairly new here, but i do have a decent understanding of stock geoketry as i have been around guns and built several centerfire guns.
first you have to understand that these guns were built when the general style of aiming was more or less "heads up" with the your chest aligned more or less parallel with the length of the but, thus all the drop in comb and butt....1-1/2 inches at the comb and 3-1/2 or slightly more at the butt was common. that in itself increases barrel jump and felt or percieved recoil, but it is somewhat offset by the fact that the guns had long, heavy barrels and that reduced jump and felt recoil because the guns were somewhat front heavy, which isn't necessarily bad if it's not excessive.....a slightly front heavy gun will hold better off-hand.
the deply curved buttplates had a function as well. they were made to be mounted on the forearm, just off the shoulder. the deep curve was there so that the butt actually hooked around and under the forearm some, so that it could be used as a "socket" on your forearm as an achor to help hold up the heavy front end. the butts were made thin, 1-1/4 inches thick was common and done that way for a reason as well. the thinner but was not so criticle to arm position and when you raised a gun to your shoulder with your trigger arm's forearm more or less straight out( level) from your shoulder, small corrections to the sight picture could be made by raising and lowering your elbow, which gave more leverage to fine tuning the sight picture than lifting or lowering the front of the gun with your "off-hand" on the forestock without imparting a canting force to the gun. it was common to hold the forestock up by placing the offhand elbow in tight to your ribcage to brace the hold and the reason they were held with your chest parallel to the forestock's length, because it put the ribcage in better position to brace the "off-hand". thus the reason the forestocks were so short, your off-hand was placed pretty close to the lock....a long forestock wasn't needed. you then made the small corrections to the sight picture by raising or lowering your other arm's elbow, as mentioned previously, letting the gun pivot up or down on your braced off-hand.
the castoff was done to bring the sights in better alignment with your eye,still keeping your heads-up posture. the consequences to that is too much cast-off also caused the cheek pad to jump up and in towards your cheekbone. a 1/4 to 3/8 cast-off was common, more can get painfull as caliber and recoil go up.
as mentioned above, pitch, the angle of buttplate to sightline is somewhat obscure with this style of shhoting as it is determined conventially, because of all the hook in the buttplates, pitch doesn't always follow any rules as conventially known. some of the earlier kentuckies and eastern penn. guns had what looks like more conventional pitch because they were shouldered in a more conventional manner. generally pitch is a balance between the stock wanting to slip off your shoulder, as in too much pitch and the stock wanting to recoil up. as in too little pitch. the right amount tames percieved muzzle jump by making the stock push straight back into your shoulder by keeping the stock on your shoukder as the muzzle jumps up at recoil. again, too much pitch and the butt wants to slide down off your shoulder making muzzle jump feel greater than it is and too little pitch drives the butt hard into the shoulder, making recoil fell stronger.
i tried to explain things as clearly as i could. some of it is pretty intertwined... i hope this helps!.
