Originally Posted by winmag
Wondering why? & wondering why it's not vastly more popular?
Among commercial cartridges, there really isn't another cartridge that does what the .270 Win does at normal hunting ranges. I am a bigger fan of the .280 Remington, but in factory form it doesn't live up to its potential. The classic .270 offers a combination of high velocity, flat trajectory, low recoil, and good terminal performance that places is squarely by itself.
I really think the original .270 is a well enough balanced cartridge that changing it around a bit tends to dim its virtue. I don't know how popular the WSM version is, but it is safe to say that it is nowhere near as popular as the original. The 6.8spc is basically a niche cartridge for AR's.
From a big picture standpoint, if you put a .270 bullet in a .308 case, it goes from being in a class by itself to being bracketed by well established cartridges to which it would offer little or no advantage and be ballistically inferior.
I say this by way of attempting to address the question you posed. I am not bashing your idea. I think it will do what you want it to do. Since you are a .270 fan, you will likely enjoy the pursuit. In the big picture, though, I think the question of why it's not more popular has a lot to do with the fact that most .270 shooters are pretty happy with the cartridge in its classic form. It's a Classic Coke vs New Coke sort of thing. We all know how that turned out.