http://www.youtube.com/watch?v=uYlte9Z9Eqk
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Another concern for using .308 ammo in a military arm meant for 7.62x51 is primer hardness. The NATO primers are harder and less likely to have an issue with some of the firearms that have free floating firing pins.
ETA: I have no fear of shooting 7.62 x 51 out of my bolt gun.
Technically they are different, but both can be safely shot in either a 7.62 NATO chamber or a .308 chamber.
If it was the 5.56 & .223 discussion, I would have said something.
What shop?
+1
CUP vs PSI....308 is loaded to a higher pressure than 7.62x51, just like 5.56 is not the same as .223 (inverse).
And I have heard of challenges when loading .308 in M14/M1A rifles for this very reason (specifically with op rods snapping). I have shot FAL and G3/CETME platforms with .308, but not very much, and they are a totally different operating system.
My $0.02.