Hi Postman
I too am having trouble regulating my 7x57R double . Its a 141 with the hex screw adjustment .
I thought I would be clever and save a thousand dollars by having my own smith install claw mounts rather than the factory but now I cant get a good group .But Im pretty sure its not the scope or mounts .
My problems are pretty similar to yours .Not so much diagonal change but separation seems unpredictable. My next strategy is to allow more time for the barrels to cool : 15 minutes rather than 5-7 minutes . I think the first two shots from cold barrels should be the guide point .The barrels seem cold but I suspect there is still some expansion .The factory instructions seem to emphasize that regulation adjustment should be from a cold barrel with a quick second shot .
Did you try different factory ammo ?
Like you I can get to about 6 to 8 inches on a lateral plane but that's at a hundred yards .
Im in for a pretty quid with this rifle as I had it restocked .
Any suggestions would be appreciated .