You may be interested in these new bullets from Wildcat bullets.
One is a standard listed bonded core flat base UP ULD design in 130 gr weight.
There is also a 140 gr Rebated Boattail ULD version in the developement stage that I will be testing here very soon in my 30" Lilja barreled 257 STW.
This bullet combined with the 257 STW's raw horse power will take the 257 calibers to ranges it has never been useful at before.
Unfortunately at 25-06 velocites, you will have some trouble with stabilizing these bulles with a standard 1-10 factory twist as least with the 140 gr ULD. The 130 gr flat base may work with top loads.
Contact Wildcat bullets at firstname.lastname@example.org
for more informtion.
These bullets have B.C. values far and away higher then any .257 bullet I know of.