Looks to me like they just made a fatter version of the 338L without basically any real improvement but ended up with a much bigger powder appetite and recoil impulse. They continually compare their ballistics to the 250gr .338 load because the 300gr .338 Lapua load performs essentially identically to the 375SP. This is, as far as I can see a HUGE nothingburger. If you couldn't do it with a .338L you still can't do it with a .375SP. Sure there's a little energy upside but not enough to say grace over.
The little brass ball... at first flush it looked to me like it was acting as a plug so when they filled the jacket with molten lead, there would be a hollow space in the nose. Turned out I was right. That little brass ball doesn't do anything for stability itself. It's just a plug and I suspect that it will be the source of a lot of consistency problems.