Question: The ballistics of the .260 Remington are basically similar to a cartridge developed in what year?

The .264 Winchester Magnum is a belted, bottlenecked rifle cartridge.  Apart from the .244 H&H Magnum and .257 Weatherby Magnum, it is the smallest caliber factory cartridge derived from the 2.85 in Holland & Holland belted magnum case.  It was introduced in the late 1950s and early 1960s with the .338 Winchester Magnum and the .458 Winchester Magnum as one of a family of short-cased 2.5 in belted magnum cartridges developed by Winchester based on the .375 Holland & Holland parent case.  It was officially introduced to the public by Winchester in 1959.  After many years of dwindling use it began enjoying a mild resurgence in popularity in the mid-2000s among long range rifle enthusiasts and reloaders due to the high ballistic coefficient of the heavier 6.5mm bullets and increasing popularity of cartridges such as 6.5mm Creedmoor, .260 Remington, 6.5 Grendel, benchrest and wildcat cartridges in 6.5mm. <SEP> The .404 Jeffery is a large-caliber, rimless cartridge designed for large, dangerous game, such as the "Big Five" (elephant, rhino, cape buffalo, lion and leopard) of Africa.  Other names for this cartridge include .404 Jeffery Rimless, .404 Rimless Nitro Express, and 10.75× 73mm.  It was created by W.J. Jeffery & Co of England based on their desire to duplicate performance of the .450/400 (3¼") cartridge.  There are two basically similar sets of dimensions for this case, depending on the manufacturer.  The .404 Jeffery as originally loaded fired a .423" diameter bullet of either 300 gr with a muzzle velocity of 2600 ft/s and muzzle energy of 4500 ft.lbf or 400 gr with a muzzle velocity of 2125 ft/s and 4020 ft.lbf of energy.  It is very effective on large game and is favored by many hunters of dangerous game.  Performance and recoil are similar to other African dangerous game cartridges.  The .404 Jeffery was popular with hunters and game wardens in Africa because it gave good performance with a manageable level of recoil.  By way of comparison, the .416 Rigby and .416 Remington Magnum both fire a 400 grain .416 in bullet at 2400 ft/s with a muzzle energy of approximately 5000 ft.lbf , which handily exceeds the ballistic performance of the .404 Jeffery but at the price of greater recoil and, in the case of the .416 Rigby, rifles that are significantly more expensive. <SEP> 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.  Other, less common names are 6.5×55mm Swedish Mauser, 6.5×55mm Mauser and 6.5×55mm Krag.  It was developed in 1891 for use in the new service rifles then under consideration by the United Kingdoms of Sweden and Norway.  The two nations had independent armies and consequently the normal procedure at the time was for their respective governments to use the same ammunition and then purchase small arms of their choice.  Norway adopted the Krag–Jørgensen rifle, while Sweden adopted a Mauser rifle design. <SEP>  Many wildcat cartridges based on the .308 Winchester case had existed for years before Remington standardized this round.  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.  When loaded with heavier bullets, the 6.5×55mm is capable of greater velocity. The .260 Remington (also known as 6.5-08 A-Square) cartridge was introduced by Remington in 1997.  Due to its shorter overall length the .260 Remington can be chambered in a shorter length action than the 6.5×55mm.