Huvius, I had the same thought, and was dissuaded by the damnably short barrels Ruger insists on putting on its No. 1s. So it would need to be a rebarrel, and then there is the matter of a reamer. Doubt many exist. Have you been happy with Bertram brass, or are you forming from something else?
Daryl, exactly so. Seems Eley had the original .375 on its hands until H&H barged in seven years later and spoilt the party.