Big Bill, Mikey, and others,
The long-raging confusion over the differences between the .308 Winchester and the 7.62x51mm NATO should have been settled long ago, but here it is in summary:
1. The 7.62x51mm NATO cartridge was developed by Springfield Armory and Winchester in the late 1940's/early 1950's in the US Army search for a standardized rifle and machine gun to replace the then-standard .30-06. .30-06 performance was desired in a smaller, lighter package that was more economical of stragegic materials and production processes.
Because the USA was the major player in the then-new North Atlantic Treaty Organization, ammunition standardization was desired, and standardization of a NATO rifle was also a goal. Ammunition chamber pressure and dimensions, case, bullet, powder, primer dimensions and manufacturing specifications were established. Rifle standardization didn't happen. You can imagine the technical difficulties of this accomplishment among some 15 NATO nations, and several dozens of arms and ammunition factories building to both English inch and metric standards. Add to that the decades-old use of ammo factory tooling and processes that were changed almost overnight!
2. Winchester released the commercial .308 Winchester in 1953-55, and established ballistics on Small Arms and Ammunition Institute (SAAMI) standards, which also specified chamber dimensions and pressure, case and cartridge dimensions.
Note that 7.62 NATO and .308 Winchester chamber dimensions vary slightly in bore, lead, and groove dimensions. The British, for example, (along with the Dutch, Germans, Belgians, and others) believed in tighter bore and groove dimensions than the US. Their small arms accuracy standards were also different, resulting in the British L1 series SLR being rated as having longer barrel accuracy life than the US counterpart, the M14.
3. To add to the confusion, nonsensical US import regulations prohibit the importation of "military small arms calibers". That is why you see ".308 Winchester" markings instead of "7.62x51 NATO" on an obviously military design such as the H&K 91/G3, CETME, FAL, etc, and ".223 caliber" markings instead of the correct 5.56x45mm NATO.
4. 7.62x51 NATO ammunition is made in several military-application versions: ball, longrange competition, tracer, armor-piercing, multiple-projectile, blank, grenade-launching, etc. These are all standardized for internal and external ballistics. Commercial .308 Winchester on the other hand, is made in many bullet weights and velocities, and these differ from one manufacturer to another.
Are they compatible? Yes, as a rule.
Are they interchangeale? Yes, within the limits described above.
HTH
John
