.243 Winchester Brass
The .243 Winchester (6.2×52mm) is a popular sporting rifle cartridge. Developed as a versatile short action cartridge to hunt both medium game and small game alike, it "took whitetail hunting by storm" when introduced in 1955, and remains one of the most popular whitetail deer cartridges. It is also commonly used for harvesting blacktail deer, pronghorns and mule deer with heavier rounds, and is equally suited to varmint hunting with lighter rounds. The .243 is based on a necked down .308 Winchester, introduced only three years earlier. Expanding monolithic copper bullets of approximately 80 to 85 grains or traditional lead rounds of 90 to 105 grains with controlled expansion designs are best suited for hunting medium game, while lighter rounds are intended for varmints.
In at least ten U.S. states and the United Kingdom, the .243 or similar cartridges are the smallest bore cartridges that are legal for hunting deer; this has been revised in the UK to allow Muntjac and Chinese Water Deer to be taken with .22 (5.56mm) chambered weapons. The cartridge can be extremely accurate to 300 yards (270 m) and beyond, but may not retain enough terminal energy to reliably drop medium game at that distance. Highly experienced hunters use the .243 Winchester to routinely drop bucks up to 250 pounds (110 kg), while less experienced hunters can be just as capable with the .243 because of its very low recoil yet high velocity. Besides hunting applications, the cartridge is popular with target and metallic silhouette shooters for those same recoil and velocity properties, with superb accuracy.
The .243 Winchester has regularly made the top five of rankings for "Best Whitetail Deer Hunting Cartridges" from sources such as Field and Stream and Outdoor Life, and its widespread popularity (called the "whitetail hunter's favorite" by the Browning Arms Company and "American favorite" by American Rifleman) assures chamberings in newly manufactured offerings of not only bolt-action rifles, but also semiautomatic rifles (e.g., Browning BAR), lever action rifles (e.g., Henry Long Ranger), and pump action rifles (e.g., Remington 7600). Gun Digest estimates that (as of the end of 2018) the .243 Winchester is the second-most popular of all hunting rifle chamberings (after the long action .30-06). Commentators such as popular ammunition author Chuck Hawks have opined that the .243 Winchester (as a "6mm NATO" round) should replace the 5.56×45mm NATO (.223 Remington) for most United States Armed Forces use cases but the .243 has, as of 2021, never been used as a military cartridge.
Above is from: https://en.wikipedia.org/wiki/.243_Winchester