The idea behind the short magnum is to have a case that fills completely with powder.
You didn't say what your seating depth is to the lands, mine is 2.823. I set mine bullets just below 2.82 so they will fit in the Remington magazine well. I have settled on using 180 gr SMKs using 70.2 grains of WXR (Winchester powder that is not a ball powder) which will compress the powder slightly. My average velocity is 3050 fps and shoots 1" groups at 200 yards off a bipod.
There is some loading data out there using H4895 that would be interesting to try,4831sc is another option, H380 and H414 wouldn't shoot in mine.
I have a couple of friends that also shoot the 300 WSM
and none of them have been able to reach 3100 fps with 180 grainers.