Brent, one of my current projects is an original high wall rebarreled to 300 WSM Rimmed, based on the 348 case in a tight-neck match chamber. My first high wall was a 6mm Remington Rimmed that I made using Norma 8x57JR brass. In between have come others in 243 Win (rimless), 223 Rem (also rimless), several Improved Zippers and my current 33 WCF Improved sporter. And of course still others in various big-bore chamberings at lower pressures but they don't really count for this discussion.
My point is that IMO the original high walls are plenty strong enough for almost any high-pressure cartridge as long as A) a modern high-tensile-strength barrel is used, B) the firing pin nose is bushed and C) normal loads are used. For an interesting perspective on just exactly how strong these actions really are, please see accounts of famed barrelmaker J.R. Buhmiller's attempts to blow them up. Articles detailing his (unsuccessful, BTW) attempts can be found in Custom-Built Rifles, The American Rifleman and others.
I have personally never seen or even heard of a blown-up high wall frame, or even a cracked one for that matter, that had not been first extensively altered or abused. Low walls yes, high walls no. Their strength, or lack of it in the case of the low walls, lies in their design and not in their material composition or heat treatment.
But anyway I respect your right to refrain from building any rifle chambered for a smokeless powder cartridge, you can just slide all those pesky old Zippers & Hornets over toward my corner!
Regards, Joe
