Well...
Did some more thinkin' on this.
Thought that maybe a .270 cartridge, on a short case like the Creedmoor, but chambered in a long action, like the 6.5x55mm Swede, so that a heavy 150 gr. bullet would seat right at the neck, and not reduce the powder charge, so you could stuff it full of RL-26 and then cork it, would be plenty sweet.
So I did some measuring and figuring and realized - That is actually the ,270 Winchester!
Seems most factory loadings have the bullet set back pretty deep.
But, if you load a 150 gr. Nosler Partition to the COL max of 3.34"...?
...the base is right at the bottom of the neck.
And P.O. Ackley already determined that "improving" the case capacity by blowing it out and changing the shoulder was a waste of time, because it just used more powder but didn't improve the velocity or performance.
Apparently, Perfect... is.
GR