The .243 Winchester was first introduced in 1955. It's based on a necked down .308 Winchester case. Bullets are available from 60 to 100 grs, giving a velocity above 3500 fps for the lightest bullet. This cartridge handles all from varmint to deer sized animals. 

This text is based on information from “Cartridges of the World”, Hodgdon reloading manual, the cartridge designer and/or own resources.