Excerpted from my article in JOURNAL #465
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. Page took one, 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. The wildcat, named the 240 Page, proved to be everything that he had hoped for - easy to form and load with both good accuracy and high velocity. He took his wildcat to both Winchester and Remington but they seemed uninterested. This was really a cover up on their part since later events have told us that they were already deeply involved in developing their own line of hunting cartridges in 6mm, Winchester on the same FAT1E3 case and Remington on the 257 Roberts case.
In late 1952 Winchester finally let the first cat out of their FAT1E3 bag by introducing the 308 Winchester cartridge. The 308, as we know, is nothing more than a commercial version of that same Frankford Arsenal case which in 1954 became the 7.62 MM NATO. Wildcatters, being who they are, immediately rallied around the new 308 case - and started looking for ways to change it. One of the first to appear 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. 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. These wildcats must have caused Winchester to reconsider the timing of their 6mm development program because there were now several wildcat cartridges threatening to pre-empt them, not just one.
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. 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 and by late 1954 everything was in place for introduction and full production of the new cartridge.
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