add up those diameters, divide by four. 0.275"
6mm 115gr, 6.5mm 140gr, 7mm 180gr, 30cal 225gr...add up those desirable, effective weights and divide by four...165grain
6mm Creed, 6.5-284, 280 Ackley, 300wm...add up their capacity and divide by four...72grs H20. Like what a 270 holds
a 170gr class .277" from a 270 Win, or a modern version would be a 270 Ackley, with a suitable twist rate to stabilize such a bullet, would be a great do-all cartridge in 2018. Sadly, only Berger offers such a projectile, the 170gr EOL Hunter (.662G1 BC). @ 2800 fps MV, which would be easily attainable from a 24" 270 Win, it really does good things downrange.
http://www.bergerbullets.com/introducing-the-berger-270-caliber-170-grain-eol-elite-hunter/
Like 25 caliber, hampered by slow 1:10 barrels, the 270 won't see much development in this area. It's a traditional caliber for fudds, and their point soft point walmart ammo. Nothing more