JCP,
Sounds great! GM is a class operation, and it's a typical example of why they're so busy!
John,
That's about as bad as I've ever heard for stupid chamberings in a Roller! Even a modern Rolling Block should never be chambered for .458, let alone a 100+ year old gun. I've seen a few chambered for other modern calibers that scare me too. Like one in .30-06!
The Rolling Block is a fine action, and stronger than some, weaker than others. Traditionally this action has always been safe with rimmed cartridges, and a small number of rimless calibers, but I'd stay away from any cartridge that develops pressures of 30,000 or more! Even in modern guns, the .458 developes muzzle energy of nearly double the .45-70 modern loads! A good stout .45-70 load is around 2500 ft lbs of energy, while a .458 Mag. runs 4500-4800 energy! That's a lot of chamber pressure!