The carbine load consisted of a 405 grain bullet with 55 grains of black powder. For a period of time, the 15 grain difference between the ‘rifle load’ and the carbine load was made up with wads that allowed the bullet to be seated to the same depth as the rifle load. Later, the filler wads were dispensed with and the bullet was seated deeper on top of the powder charge.
Initially both the rifle and carbine loads used 405 grain bullets. THe “R” for rifle and “C” for carbine was needed to distinguish between the two types once removed from the original packaging.
When the rifle cartridge was changed to a 500 grain bullet, which extended much further from the case mouth, the two types were easy to identify, and the R /C markings were dropped.
Your cartridge would be the 45-70-500, fourth from the left. The Carbine cartridge, the 45-55-405 is fifth from the left.
The “R” and “C” were not dropped from the headstamp until 1886 when the carbine bullet was seated deeper - cartridges sixth. and seventh from left.