You should use Magnum primers for better ignition. Because the 7mmM is one of the Large Overbore calibers, it prefers slower powders. H4831 and SLOOWWEERR. Magnum primers are used to get it going. I am getting ready to try some RE25 and Retumbo in mine. IMR7828 is also a good one to go with. I will be pushing a 160grn Nosler Partition down my tube.
Just got myself a Ruger No.1. Had an M77II in 7mmM. (that one is at HART for a 300WM tube).
Put em in at the bench and send em down the bore