We started using the .243 Winchester in a model 70 rifle specifically for hunting the Columbia Blacktail deer in Northern California back in 1956 and have had one ever since. We compared it to the Remington .244 in a model 722 and found the .243 to be a much easier cartridge to reload accurate loads for. There is an excellent article on the .243 Winchester on the GunnersDen.com web site.
From: .243 Winchester. (2009. February 28). In Wikipedia, The Free Encyclopedia. Retrieved 15:27. March 16, 2009. from http://en.wikipedia.org
"The .243 Winchester is a very popular sporting rifle round. It is ideal on game such as Whitetail deer, Mule deer, Pronghorn antelope, Black bear and wild boar. In the USA it is very effective for long range varmint shooting. It uses what is basically a .308 cartridge case necked-down to accept a .244 in/6 mm bullet. The .243 is well known for its accuracy, very flat trajectory, and relatively mild recoil compared to other cartridges. In Southern Africa the .243 was voted as the most popular hunting cartridge in South Africa, Namibia and south-western Botswana, because of its long range capabilities and effect on game in the Springbok/Blesbuck category where ranges can reach in excess of 300m.
This cartridge was first introduced in 1955 for Winchester's Model 70 bolt-action sporting rifle, and it quickly gained popularity among sportsmen worldwide. Even Winchester's chief competitor, Remington, was quick to chamber rifles for the .243 round, and all mass-market rifle makers have followed suit. Many companies offer a selection of rifle models chambered in .243 Win.
Since the enactment of the 1963 Deer Act in Great Britain, which stipulated a minimum bullet diameter of .240 in together with minimum levels of muzzle velocity and bullet energy, the .243 Win. has been perceived by UK sportsmen as the "entry level" caliber for legal deer-stalking; and since the 1960s the .243 has been by far the most widely used caliber for shooting small and woodland deer in the UK.
Firearms that would normally be chambered for the .308 Winchester/7.62x51mm NATO caliber are distributed chambered for the .243 cartridge in Countries whose regulations restrict or forbid civilian ownership of "military calibers"; examples of countries with such legislations are France and Spain.
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, plus slightly lengthens the case, giving about 10% more powder capacity, and some small improvement in velocity. Both versions of the .243 cartridge are good for hunting deer."