My friend, Les Hawkes was in John's shop when Roy WTBY showed up one day. John was testing a new .458 magnum he'd wildcatted using the .378 WTBY case, a simple neck up. He had a 3'diameter x 4' long chunk of oak in the shop & had just shot through it with the .458. (Who knows how chewed up inside it was).
John showed Roy the case and noted it would not shoot through the chunk with a full powered load, 500gr. solid at 2,650fps (or so), but he reduced the vel. to 2,400fps and shot right through it. I do not recall the 'make' of that bullet.
Earlier, when Les Hawkes had walked over that morning, John had a spotting scope in the window looking across the street at the buildings. John said, "get in here, I just shot through that oak with my new .458". Les said John was looking for holes in building across the street. It was fairly early and the street was clear. Les said the "folks were used to loud bangs around there")
About an hour later, is when Roy W. showed up. John showed him his "new .458". Roy was given a case(perhaps).
A month or two later, Roy introduced his .460 WTBY Magnum on the same rifle as his .378 mag.

To "get into shape" (toughen up) for his African Trips, Les said John used to shoot a SxS .450 Express. He had a block of wood between the triggers, so both barrels would go off when pulling the front one. I'm fairly sure it was a BPE. That would be a lot less expensive 'shooting' than a nitro rifle.