I think you will struggle with 300gn bullets in the 300wsm case! The 300wsm case is all about efficency with 180's or less. 200's at a pinch.
These big pills needs lots of slow burning powder and you dont have that capacity in the 300wsm case.. 69gn is already compresses with 180gns.
Better have look at the 338 Norma for an efficient design. Just do a quick search here. Or just buy a .325wsm in my opinion. The big W went for the 8mm or 323 diam instead of the .338 for a good reason as they had a tough time getting .338 win mag performance. No hope with the 300gn or even 250gn pill IMO.
If you want to shoot 300gn bullets I think you will need a lot bigger case.
I could be wrong but I have played with enough wsms to realise were their efficiency lies. They are efficent and accurate and use less powder to a point!