Not to argue or stir up crap, but I find it hard to believe the Handi won't handle the 460 SW at 60,000+ when the rifle is chambered for hot numbers like the 270 and 25-06 that operate in the same pressure window. There is only .008" difference in the case body diameter between the '06 family cases and the 45 Colt family cases. At the same time, the 500 SW is rated to the same 65,000 psi by SAAMI and NEF chambers for it, not to mention the many 45-70's that are run with Ruger #1 loads that make as much as 50,000 psi. I see no good reason not to chamber to 460 SW, run it on a diet of 45 Colt/454 Casuell loads and on hunting excursions load it with the 460.
In external ballistics the 45-70 will always be superior to the 460, but because of case volume, the Colt/Casuell/SW case will always be more effiecient and make for a far friendllier plinker.
Were I not so dead set against ever owning another NEF, I'd get one of these 45 barrels and do exactly this with it. As it is, a 460 barrel for my TC is on my "gonna get one" list.