Rabbit-
How firearm recoils can have a dramatic influence on point of impact. I used to compete in police revolver matches years ago. When I first started shooting all the old timers were very well versed in this. If my .357 was sighted in for the high velocity .357 rounds and I forgot to adjust the sights for the 38 wad cutter, contrary to what common sense dictated, the revolver shot high with the slower moving target round. The reason? Even in my 4" barreled revolver, the slower moving projectile was under the influence of recoil. Now whether this actually carries over to shotguns, I do not know, 1,200fps is considerably faster than the .38 target loads, on the other hand 28" of tube is considerably longer than 4".
With that said, like you, however, I am not totally sold on the recoil/point of impact theory. When your eye is your rear sight, how the gun is angled (the pitch) should, in theory have a great influence on where the shotgun shoots.
The photo below is of the stock of one of my shotguns. Before adding the pitch spacer, the shotgun was very uncomfortable for me to shoot and I was shooting it badly. I allowed a friend to shoot it and without being prompted, he said, "this thing recoils funny," and it did. The gun slipped* off the shoulder under recoil and I had a hard time hitting anything with it.
When I compared the shotgun to one I shot well (my Fox SW), I noticed the pitch was very different. So using the Fox as a rough guide, I calculated the pitch and installed a pitch spacer on the offending shotgun. Measuring the 30" barreled shotgun from the wall now gives me 1 1/2".
On the general issue of pitch, I am just a regular guy without any great mechanical skills or contraptions, so my approach was not exactly scientific, mind you. but it worked for me (“if it is stupid and it works, it isn’t stupid”). My approach was to find a shotgun I shoot well and make the other one as much like it as possible.
Doug
*edit by "slipped" I mean to say the pad was slipping down toward the arm pit and the barrels "bouncing" up.
