This is from AmmoGuide http://ammoguide.com
If you reload it is a good resource. Costs 18.95/yr and is worth it.
The original cartridge was developed by the Ordnance Dept. of the U.S. Army in the 1940's through 50's under the name T-65. After extensive testing, it was to become the first NATO-adopted "standard" cartridge, the 7.62mm NATO, or 7.62x51mm.
Winchester requested and received permission to introduce the cartridge commercially as the .308 Winchester. The result has been worldwide acceptance in a range of sporting firearms. However, the 7.62x51mm NATO and .308 Winchester should not be considered interchangeable. More on that below.
The military endeavor was to improve upon the .30-06 Springfield round, which had been in service since 1906 (or 1903 if one considers it's real origin as the .30-03). The result was a round of substantially less weight and size, while retaining the same bore diameter as well as only a negligible drop in ballistics (muzzle velocity was within 100 fps of the larger round).
The .308 has been neck-sized successfully to a variety of commercial calibers. These include the .243 Winchester, the 7mm-08 Remington and the .358 Winchester. All are excellent choices for short-action rifles, covering a wide-range of applications.
Key differences exist between military and commercial designs, notably in the hardness and thickness of the brass as well as the external dimensions of the case itself. The shoulder and neck of the military design dictate they are farther from the rim by .013 inches (commercial spec shown above), resulting in a significantly different headspace situation between the two rounds. The combination of shorter commercial ammunition in the slightly longer military chamber presents a possibly dangerous situation due to the emergence of a gap in the mating of case and chamber shoulder surfaces.
Even if military cases are shaped to the commercial chamber, it's reloading characteristics are different from commercial brass. The increased thickness of military brass results in more difficult sizing operations and reduces available powder capacity. This has the effect of increasing pressures when using military cases, with like charges. Also, primer pockets are likely to be crimped, complicating priming and de-priming operations. Nonetheless, some precision target shooters are careful to deal with these issues and prefer military "Match" 7.62x51mm cases, fire-formed to their chamber.
The .308 Winchester family can be viewed here: