cases but not until the 2020 release of the 6mm ARC did a .243 caliber cartridge find limited adoption by the US Armed Forces. History Well-regarded Field and Stream editor and Harvard-educated technical gun enthusiast Warren Page began experimenting with wildcatting a .243 caliber (6.2mm) round in the 1940s sometime after the 6mm Lee Navy was discontinued. When the .308 Winchester was introduced in 1952, Page started necking down the .308 design into a new .243 wildcat cartridge. After Page's hunting success with and much writing about this new version, Winchester developed a factory loaded .243 soon thereafter. It was first introduced in 1955 for the Winchester Model 70 bolt-action and Model 88 lever-action sporting rifles and quickly gained popularity among sportsmen worldwide. It was a ground-breaking development with at first only two factory loads, combining a versatile and effective combination of 80-grain bullets optimized for high-velocity, long-range performance for varmint hunters (e.g., groundhogs, coyotes, prairie dogs) and 100-grain bullets suitable for game up to the size of deer and pronghorn antelope. Its predecessor in the Winchester lineup, the very similar .257 Roberts, could have easily been selected to accomplish the same tasks, but was not available factory loaded with either lighter, varmint-weight bullets or pointed, long range spitzer (pointed) bullets, so it never achieved the popularity of the newer round. Remington also saw the 6 mm (.243 in) family as suitable for this dual-purpose use and introduced their version, the .244 Remington, in the same year (1955) based upon the .257 Roberts necked down to accept .243 bullets up to 90 grains in weight. The Winchester round remains available today whereas the .244 Remington, later renamed the 6mm Remington with the introduction of 100-grain bullets, is far less popular even though it can push all bullet weights slightly faster with maximum loads due to the larger capacity case. The fact that the .243 Win was originally offered in a 1 in 10 inch rifling twist rate, a rate better able to stabilize heavier, 100- and 105-grain bullets, versus the .244 Remington's 1 in 12 inch twist (hence the 90-grain factory offering) was also a factor in their popularity. Since the enactment of the Deer Act 1963 in the United Kingdom, which stipulates a minimum bullet diameter of .240 inches, together with minimum levels of muzzle velocity and bullet energy, the .243 has long been perceived as the entry-level caliber