LVSteve
Well-known member
Doncha just love how certain inaccuracies become fact and refuse to die no matter how many times the truth is spoken. Yes, it's 7.62 NATO vs .308 Winchester AGAIN. Shooting Times trotted out the old fiction about .308 Win being a 62,000 psi cartridge and 7.62 NATO is only 50,000, so has much less pressure. WRONG,WRONG thrice again WRONG.
The 62,000 psi figure for 308 Winchester is the latest SAAMI pressure measured using a piezo pressure transducer. The value for 7.62 NATO comes from an old Copper Units of Pressure (CUP) style measurement, and the answer is indeed 50,000 CUP. It's like saying the distance between two points is 62 miles and somebody says, "No, it's much further, like 100 km". Unfortunately there is no "laws of physics" based PSI to CUP conversion, but empirical data does show a relationship. http://www.shootingsoftware.com/ftp/psicuparticle2.pdf
Shortly, somebody will appear and say "Ah, but it's 50,000 psi CUP". There's no such unit of measure. It's like measuring your inseam in grand pianos per decade. Don't go there.
If you compare .308 Win and 7.62 NATO as specified by the European standards folks at CIP, Commission Internationale Permanente pour l'Epreuve des Armes à Feu Portatives - Wikipedia, the free encyclopedia, lo and behold they are both rated at the same pressure. C'mon now, you're not really surprised, are you?
Yes, the SAAMI spec for the .308 Win CASE is not the same as that for 7.62 NATO. The latter has thicker walls at the head for use in automatic weapons with generous headspace, so it has a little less capacity than .308 Win. Big deal. Go look at the velocity specs listed by any of the big manufactures and you will see they are usually identical for bullets of the same weight. Does that sound like the extra case capacity is making much difference, or that one runs at 20% more pressure than the other? No, it doesn't work for me, either.
The 62,000 psi figure for 308 Winchester is the latest SAAMI pressure measured using a piezo pressure transducer. The value for 7.62 NATO comes from an old Copper Units of Pressure (CUP) style measurement, and the answer is indeed 50,000 CUP. It's like saying the distance between two points is 62 miles and somebody says, "No, it's much further, like 100 km". Unfortunately there is no "laws of physics" based PSI to CUP conversion, but empirical data does show a relationship. http://www.shootingsoftware.com/ftp/psicuparticle2.pdf
Shortly, somebody will appear and say "Ah, but it's 50,000 psi CUP". There's no such unit of measure. It's like measuring your inseam in grand pianos per decade. Don't go there.
If you compare .308 Win and 7.62 NATO as specified by the European standards folks at CIP, Commission Internationale Permanente pour l'Epreuve des Armes à Feu Portatives - Wikipedia, the free encyclopedia, lo and behold they are both rated at the same pressure. C'mon now, you're not really surprised, are you?
Yes, the SAAMI spec for the .308 Win CASE is not the same as that for 7.62 NATO. The latter has thicker walls at the head for use in automatic weapons with generous headspace, so it has a little less capacity than .308 Win. Big deal. Go look at the velocity specs listed by any of the big manufactures and you will see they are usually identical for bullets of the same weight. Does that sound like the extra case capacity is making much difference, or that one runs at 20% more pressure than the other? No, it doesn't work for me, either.
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