If I wanted a 270Wby, I would just build a 270WSM and eliminate expensive brass, a belted case and a longer action and still have the same ballistics.
Not quite
270 WSM is a little warmer then a regular 270 win .
If it were my choice it would be the 270WBY or the 257 WBY
I guess it depends on your definition of "little," and how "warm" you load your 270 win. I have owned four different 270WSM's and two different 270Wby rifles. The only significant gain in velocity in the Wby was with 150 grain bullets, and that amounted to about 120fps. The one and only 270 Win I own shoots almost 300fps slower than the average of my 270WSM's using the same projectile. Sure, it's a small sample of 6-7 rifles, but the results are real. I understand that the WSM's are not a hot commodity on this forum, and I am not saying that they are the greatest thing since cold beer either. What I am saying is that it is possible for someone, not you specifically, to be biased, one way or the other, for certain rifles and/or cartridges, and that can end up misleading others who read the thread.
Just for information, here are my load results:
270 Win, 140 Accubond, 2984fps 22" bbl-1 gun average
270WSM, 140 Accubond, 3260 fps 24" bbl-4 gun average
270Wby, 140 TSX, 3275 fps 26" bbl-2 gun average
These were what I considered max in each rifle, and were final hunting loads with acceptable accuracy. No load is over published maximum.
With that aside, the .264 Win Mag still sounds like fun, and I would also like to try the .257 Wby.
