The marlin 45-70 loads are kept down to 28000 cup where the 450 Marlin are loaded to 42000 cup. As stated above the rifles are of the same strength and handloaders can take advantage of the stronger rifle. The 45-70 loads from the factort must be kept down 18000 cup or less to respect the old trapdoor springfields strength. The 450 arli, I think has a Belted case to prevent being chambered in a 45-70.