IIRC the 30-378 has a brass rim dia of .579" and as such would be a bit too much for the Savage bolt head to handle IMHO. You could build one on a Savage Lapua action and should be strong enough but I am not sure even at that if you would be able to have a repeater with the OAL being that long it may not fit in the mag anyway.

If it were me I'd go with a 300 RUM and even at that you would have to have the mag well opening milled out to be able to use the longer SF mag or you could modify a CF mag to handle the RUM.