The ballistics of the .260 Remington are basically similar to a cartridge developed in what year?
.260 Remington:  Although loaded to higher pressures, the ballistics of this cartridge are basically similar to the 6.5×55mm when bullet weights do not exceed 140 grains. 6.5×55mm: The 6.5×55mm (designated as the 6.5×55 Swedish by the SAAMI and 6,5 × 55 SE by the C.I.P.) is a first-generation smokeless powder rimless bottlenecked rifle cartridge. 6.5×55mm:  It was developed in 1891 for use in the new service rifles then under consideration by the United Kingdoms of Sweden and Norway.
i don't know