If you're looking for a more classic Call of Duty experience, then you should start with one of the earlier releases, such as Call of Duty 4: Modern Warfare.
If you want to play the CoD games in the order they came out, this is the order you'll want to follow: Call of Duty (2003)Call of Duty: United Offensive (2004)Call of Duty: Finest Hour (2004)
308 Winchester cartridge as a base, the round was modified slightly. They wanted to eliminate feeding issues and to reduce overall cartridge pressure . The 7.6251 or 7.62 NATO (which is another common name for the caliber) was officially introduced into military service in conjunction with the M14 rifle.