It seems that you've exhausted the possibilities with various seating depth and 4350 but it's not getting you where you want to be..

I'd be looking at 7828 or H1000 to get those long bullets up to speed in a Swede.

I briefly had a Ruger in 6.5x55 but the majority have been M96 and M38. Slower burning powder helped me find more consistent loads in my Swedes.

Good luck with the project!

"Camping places fix themselves in your mind as if you had spent long periods of your life in them.
You will remember a curve of your wagon track in the grass of the plain like the features of a friend."
Isak Dinesen