The steel head is a replacement for a belt.
Belted ammunition can handle far higher pressures but still only reach about 65,000 PSI.
Nope. sorry. Belts got nothing to do with cartridge power. There are plenty of 65,000 psi cartridges that aren't belted, and zero belted cartridges that can withstand 80,000.
Belts originally were added to aid in maintaining headspacing & extraction in slick-feeding rimless (usually straight-walled) cartridges. Then it became a "trademark" of the magnum cartridge, but that was all marketing hype (thank you, Roy Weatherby).
Belted Magnum Cases: A Myth Dispelled
By Philip Massaro, July 16, 2014
"...That beautiful belt has nothing at all to do with strength; it serves to function as a means of headspacing...."