Well I went for a trawl through my library, and admittedly there is not much about. How 'bout this though, for the .450 straight, from page 132 of Greame's 2nd edition:

Load 5: 52gr 4198, 350gr CAST, 1930fps, 7.5 tons
Load 6: 52gr 4198, 350gr JACKETED, 1860fps, 8.2 tons

Primers, cases, dacron filler, and proof barrel same for both.

By my reckoning, that makes jacketed bullet pressures higher than lead bullet pressures. Matching the lead-bullet VELOCITY with a jacketed load would push the pressures even higher.

On the Zabala 10-bore, I measured it across the breech-face and it is NARROWER than the Empire 12-bore. I will measure it again when I get the chance, to check the height of the standing breech, but at first glance this would indicate that the chamber-walls could be made thicker with the 12-bore action. Also, the long action-bar reduces the opening forces on the bolts, but whether this is more important than bending forces on the bar itself is anyone's guess.

I really can't understand why you have a problem with this, 470R. It Works. QED!

BTW, here is a pic of the (relatively) new Woodleigh 650-grain steel-jacketed solids. Jewellery for boys!
I will give them a run against buffalo when the barra-fishing subsides, but don't expect to get many bullet-recoveries!