Today, it is offered as an option for most rifles that can take .308 Winchester cartridges; all that is needed is a barrel change, as the length of the cartridge and rim diameter (which would affect the bolt) are nearly the same.
The .243 Winchester, being derived from a .308 Winchester cartridge, uses a case that is the same length as the .308 case, and a bullet that is also the same length as a .308 bullet (51mm); the case is necked down to accept .243 caliber (6.2mm) bullets. The .243 is rimless, and uses a large rifle primer.
Bullet weights generally range from 55 grains to 105 grains; the lightest bullets have an average muzzle velocity of very slightly over 4,000 feet per second. Because of this, the cartridge tends to have a very flat trajectory.
The .243 Winchester is best fired in a barrel with a 1:10 rifling twist, and fires with a maximum pressure of about 59,000 PSI.