You can order a RUM rifle from the Savage custom shop, they still build them. It won't be on a Lapua action, but a large shank long action. Hodgdon shows loads for the 300 RUM going all the way up to 63,900PSI. If Savage didn't feel it was safe to do so, I seriously doubt they'd sell you a rifle in the RUM chambering. Going an extra 2000psi in the 30/378? You might just be treading on thin ice there.....