Re: Rifle canting, crosshairs not well aligned,
I understand the concepts and ideas your work supports. I have two old external adjustment scopes both with parallax adjustment that I use on my old Winchester 52C and Remington 40X .22lr target rifles. One is a Fecker 16x made in the 1940's and tho other a Unertl 20x made in the 1960's. Both have spring systems to allow recoil control for big rifles too that isn't needed in the 22. These are old enough that the crosshairs may actually be spider silk. I don't know for sure. Zeroing one at 200yds in a 22lr does move them off center a ways.
If I had the experience that you do I might try barrel bending but really haven't seen the need as neither of my air rifles appear to have too much droop. Since I don't like or shoot break barrels I haven't tripped over that problem too much. Although I have dropped rifles, and myself in the dirt more than once over the years.
Where did you find the drawings that you show here? I would like to get a copy of the reference from which they were taken for my library. Source?
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RWS54, 4.5mm, RWS 4-12x50CI
FWB300SU, 4.5mm, Clearidge Ultra RM 3-9x32