The reason that we have new cartridges is that, for the western hunter, many old cartridges are [bleep]. A .30 Nosler fits in exactly the same rifles as a .30-06, but substantially extends the ranges at which game can ethically be hunted.
New cartridges are generally caused by one of the following:
Moving to a shorter action or replacing a cartridge that was designed for an odd size intermediate action for which good actions are not available
Moving off an incorrectly chosen slow twist to a correct fast twist
Removing a counterproductive belt
Cartridge shoulder/taper improvement giving better performance for less recoil
Fixing an OAL, shoulder position, or throating problem
Complying with specific state hunting regulations
Strongly disagree. The ranges where game can be ethically hunted? The same variables still apply including weather, game behavior, and hunter shooting ability. The 300 Win Mag will allow one to kill at the same range as the 30 Nosler. That does not mean most hunters have any business shooting that far.
