Windage adjustment off center?

Have you tried swapping the sights from gun to gun to see if the windage setting changes on each gun?

Maybe the sights aren't fitting the dovetails quite right and swapping them from gun to gun might improve things a little.

EDIT: Sorry. Deleted the part about the stock. My mind has been a mess the last few days and not thinking straight. Also added the bit about the dovetails above.

you would have to find dead center on the sight and on the dovetail and see if they match 

if the sight is not mount dead center on the tube you have your answer and of course is the barrel dead center to the dovetail on the tube 

but in the long run if you can get it to work, you don't have a problem just a question  

head position and a diopter iris now that is an interesting question, i don't know 

Just a tip, the barrels on the 77s actually bend pretty easily. 

The FWBs are MUCH harder to bend. 

Posted by: @specie

For my FWB 150 with Walther LGV aperture sight and HW77 with Anschutz 6700 sight the windage is far from center. I don't see how the barrels can be bent to the side on these guns. Is there another explanation?

My guess is a canted or off-center front sight.