Lone Star, Ruger also lists the No.1 in .416 Rigby with case dimensions very close to that of the .378 Weatherby Magnum. Of course, the chamber pressure of the .416 is 46,000 psi vs 60,000 for the .378 Weatherby. The .458 Lott's pressures are more like 53-55,000 psi. In any case, the No.1 can handle it.