I have never seen any indication of incipient case head separation in the 45-70. And I have loaded some of the first Winchester 45-70 brass I bought in 1977 100 times. Split case mouths/necks are the usually the failure in 45-70 brass I experience and that condition is reduced by annealing when necessary. It is my guess that 45-70 brass will last for just as many loadings as 450 Marlin brass as they are about the same thickness in the neck. Hence, I think the only problem the 450 Marlin was designed to address was creating a 45 caliber lever gun rifle cartridge that equaled the potential of the 45-70 in the Marlin lever gun yet could not be chambered in a 45-70 or a standard magnum.
