Jimmy,
Unfortunately there is no easy answer. Books and Articles entitled "Overloading the 7x57/7mm Mauser/.275 Rigby to 65K PSI" aren't there.
I treat "modern pressure metrics" (7x57 and 6.5x55 in my case) like wildcats. I use Quickload and check the estimated velocities and pressures against known loads and book data for cartridges of similar capacity in the same caliber. Application of JB's "Rule of 1/4" and testing with a chrony provides a sound reality check for load development.
If you don't want to play ballistic pioneer, that is totally understandable. Either kill LOTS of things with the 7x57 loads that equal factory performance OR shoot a 270, the passe' round whose performance we are all trying to equal with our 6.5's and 7's in the first place.
GE
7mmEDC #2
