Yes, you can use 300wsm, because when you run it through a fl sizing die, it creates a false shoulder. Stay away from 270wsm though, because you would run the risk of case separation, due to excessive headspace.
How would 300 WSM brass work and 270 WSM not work, when they are both the exact same shoulder length? The 300 would neck down, but you could easily neck up 270 to do the same thing. And BTW, all this is a very BAD idea! I've seen case heads separate on much less than .038" expansion.
Someone who "knows" as "much" as you,is going to be farrrrr better served by asking questions...rather than giving "answers". Hint.
Now as to Montucky 7 Whizzum's,I've only got a trio and reckon I should salt a few more away,if only for good measure. They've the RPM,throat geometry and COAL latitude,to connect all dots and are without doubt,the most Superb Killing Rifle ever offered over the counter and I've mused same more than a few times.(grin)
The Montucky Whizzum handle is rather adept in managing felt recoil and Sister has loved her's,since a pre-teen. I savvy the appeal.
Puked another set of LW's on one,not long ago and I think that's (8) sets that've puked on me...outta about 40 that were in service as mainstays. Though in fairness,this is the first puke,in that location and different from most other LW failures. Admittedly,said rifle is a Safe Queen.(grin)
Lapped Of Course...RINKJust sayin'.
Swore off LW's all together and started tossing schit offa cliff.
I hear good thangs about 180 ELD's in same(2950fps),though the 162 'Max and 162 ELD's ain't no slouch(3125fps)...or so I've heard.
'Course I VERY much enjoyed your keen "understanding" of headspace,as you talk out your ass about the things furthest from your faculties...so PLEASE continue with your version of "knowledge","experience" and "results".
Hint.
Just sayin'.
Bless your heart.
Laffin'!
Wow +P+!