So I was trying to make up a GMX load for my 7 mag I tried some Retumbo not so good I was gonna head toward some 4831 and see if I can get anything better. Any suggestions for a 139 gmx in a 7 mm mag please let me know what works for you.
I don't have any experience with this combo, but Retumbo is too slow for that bullet and cartridge combination. I would definitely try 4831 or even 4350 and see if you get the speed and accuracy you are looking for.