No one loves their 7.62x40WT more than I. However, if I was going to build something new it would be chambered in 300 HAM'R.
Frankly, I'd ask them about doing a 300 HAMR. The main difference is in throat length, which helps with the 150s but does nothing for the 125s. I'm running a XCaliber 5R using less powder with 125s and get 100fps more than the 300 data shows.
They are arguably all but identical cartridges. There's only a millimeter (.040") difference in case length.
