I think I identified your problem. Win 540 is a SHOTSHELL powder and also suggested for use in 10 mm Auto carts (according to the Seirra manual). I would switch to these other powders:

IMR 3031, 4064
WIN 748 or 760
Hodgdon H-380, Varget, or BLC 2
Hurcules Re15

The burn rate on the Win 540 you are using is not proper for your round rifle combo. Ihave used all of these powders except for Varget and BLC2. They all gave less than 1" in my rifle. I get best results in my rifle from IMR 3031, H-380, and Re15. I shoot a .308 too.