I think the 375 Ruger has more or less been adopted as the best option as a parent case.
My experience with the 280 was never the best.
One rifle, a Lancaster shoots wonderfully although it’s a bit of a beater.
My old Gibbs (magnum Mauser) was way over pressure with the same loads that shoot so well in the Lancaster.
Another 280 I had also flattened primers and produced a hard bolt opening with loads that should have been acceptable so it went down the road too.
I still have probably 1000 .287” fmj SP bullets which I’m sure are military projectiles as well as some other sporting bullets if anybody in the States needs some.