Condensed from my article in JOURNAL #465
Conventional thinking says that the 243 Winchester was introduced in 1955 and is nothing more than the 308 Winchester necked to 6mm. But the cartridge actually evolved from two seperate directions, wildcat and factory, at the same time.
It started in 1951 when rifleman, wildcatter, and writer Warren Page mysteriously got his hands on some Frankford Arsenal Light Rifle experimental brass designated the FAT1E3, a.k.a. the T65. Page took a case, ran it through various loading dies until he had what he thought was a reasonable neck length and what appeared to be a 30-degree shoulder. He sent that sample case to his reamer grinder and told him to make a set of reamers “. . . just like that. No calculation, no dimensional hairsplitting . . . ” The resulting wildcat was named the 240 Page.
Page was convinced that the time was right for a 24 caliber cartridge from one of the major US companies and he took his wildcat to Winchester’s R&D department (Page was Shooting Editor of Field & Stream Magazine at the time, a position of some prestige) but they seemed uninterested. This was really a cover up on Winchester’s part since later events have told us that they were already deeply involved in developing their own line of hunting cartridges based on the Frankford Arsenal case. In late 1952 Winchester finally let the first cat out of their own FAT1E3 bag by introducing the new Model 70 Featherweight Rifle chambered for the equally new 308 Winchester cartridge. Wildcatters, being who they are, immediately rallied around the new 308 case - and started looking for ways to change it. One of the first offspring to appear, in 1953, was very much like the 240 Page but retained the 20-degree shoulder and short neck of the parent case. It was dubbed the 308-6mm, and was soon showing up in the varmint hunting fields. A similar design, the 6-308, used the 308 case necked to 243 but pushed the shoulder back slightly to create a one caliber neck.
The first Winchester 6mm cartridges that I am aware of are made from what appears to be US Ordnance Department Project SALVO brass headstamped WCC 54. It is not clear if these cartridges were part of SALVO itself or simply Winchester using excess brass that it had at its disposal. SALVO did test 18, 22, 25, 27, and 30 caliber cartridges based on the Light Rifle case but I cannot find any reference to a Cal. 24 for Light Rifle. The 6mm case appears identical to all of the other SALVO Light Rifle cases in every dimension except for bullet diameter. The WCC 54 cartridges were soon followed by unheadstamped prototypes. Later that year (1954) at least a couple of experimental varmint-weight Model 70 rifles were manufactured for field testing (one by Warren Page of all people) but chambered for the cartridge they now called the 6mm WINCHESTER. Properly headstamped cartridges were produced.
By late 1954 everything was in place for introduction and full production of the new cartridge. But you have to remember, in the 1950’s United States, metric cartridges, including wildcats, particularly in 6mm, were almost unheard of. The metric system was, for the most part, abhorrent to the U. S. and the idea of a new 6mm with the big “W” on it was probably the cause of much anguish in Winchester’s marketing department. So, at the last minute the metric designation was abandoned, the cartridge was renamed the 243 WINCHESTER and it was introduced in 1955.
By the end of the 1950s the 243 Winchester had grown in popularity and the wildcats were all but forgotten. But as good as the Winchester cartridge is, time has shown us that Page’s original design was even better. In the late 1990s the circle was completed when several nearly identical competition wildcats were developed and successfully used by shooters who knew nothing of the 240 Page of forty-five years earlier.