That's going to take quite a die set to neck the .458 SOCOM all the way down to 6.5mm....and don't forget, you won't be able to run the pressure to 50k either, or the lugs are going to come off the bolt. A 6.5 at 35k on the SOCOM case would be slower than a 6.5G or a 6.8. Your suggestion is a poor one.
Tony
