| .243 Winchester Improved (Ackley)|
The .243 Winchester (6×52mm) is a popular sporting rifle cartridge. Initially designed as a varmint round, it may be used for wildlife and game such as coyote, blacktail deer, whitetail deer, mule deer, pronghorn, and wild hogs. It can also be used against larger game such as black bear or elk, but is sometimes said to be "too light" for such large game. Rounds of at least 90 grains are better suited for hunting larger game while rounds less than 90 grains are more suitable for varmints. The .243 is based on a necked down .308 cartridge case.
.243 Winchester Wikipedia
This cartridge 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. Just about every major manufacturer offers rifles chambered in .243.
It was a ground-breaking development of the day, combining a very useful combination of lightweight (70 to 85 grain) bullets optimized for long-range performance for varmint hunters (groundhogs, coyotes, prairie dogs) and 90 to 105 grain bullets suitable for game up to the size of deer and pronghorn antelope. Its predecessor in the Winchester line-up, 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 pills or pointed, long range spitzer (pointed) bullets, so it never achieved the popularity of the newer round.
Remington also saw the 6mm (.243") 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" rifling twist rate, a rate better able to stabilize heavier 100 and 105 grain bullets, versus the .244 Remington's 1 in 12" 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 stipulated a minimum bullet diameter of .240 inches, together with minimum levels of muzzle velocity and bullet energy, the .243 is now perceived as the entry-level caliber for legal deer-stalking. Firearms that would normally be chambered in .308 Winchester/7.62×51mm NATO are sometimes available in .243 in countries–such as Spain–whose regulations restrict or forbid private ownership of so-called military calibers. No military is known to currently designate this round for service.
In a non-sporting context, bolt-action rifles chambered for the .243 were utilized by the Los Angeles Police Department's Special Weapons And Tactics (SWAT) unit during its early years.
P. O. Ackley created an improved version of this cartridge called the .243 Winchester Improved (Ackley). Like other improved cartridges, this created a steeper shoulder and blew the sides out, giving about 10% more powder capacity, and some small improvement in velocity. Both versions of the .243 cartridge are good for hunting deer.
The .243 produces a velocity of 2,960 feet (902.21 m) per second with a 100-grain (6.6 gram) projectile from a 24-inch (610 mm) barrel. Commercially loaded .243 ammunition is available with bullet weight ranging from 55 grains (3.6 g) up to 115 grains (6.8 g). Twist rate of barrel is the major deciding factor in which bullets to use, 1:10 being the most popular as it is sufficient to stabilize up to 100-gr. bullets. However, for VLD (very low drag)-profile and bullets heavier than 100 grs., a 1:8 or 1:7 (for 115-gr. VLD bullets) is necessary.