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Old 10-31-2012, 02:11 PM   #11
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.223/5.56...........
According to the official Commission Internationale Permanente pour l'Epreuve des Armes Feu Portatives (C.I.P.) guidelines the .223 Remington case can handle up to 430 megapascals (62,366 psi) piezo pressure. In C.I.P. regulated countries every rifle cartridge combo has to be proofed at 125% of this maximum C.I.P. pressure to certify for sale to consumers. This is equal to the NATO maximum service pressure guideline for the 5.56x45mm NATO cartridge.

According to the official NATO proofing guidelines the 5.5645mm NATO case can handle up to 430 MPa (62,000 psi) piezo service pressure. In NATO regulated organizations every rifle cartridge combo has to be proofed at 125% of this maximum pressure to certify for service issue. This is equal to the C.I.P. maximum pressure guideline for the .223 Remington cartridge, that is the 5.5645mm NATO parent cartridge.

.308.7.62............
Although not identical, the 7.6251mm NATO and the commercial .308 Winchester cartridges are similar, and even though the Sporting Arms and Ammunition Manufacturers' Institute (SAAMI) considers it safe (by not listing it) to fire the NATO round in weapons chambered for the commercial round, there is significant discussion about compatible chamber and muzzle pressures between the two cartridges based on powder loads and wall thicknesses on the military vs. commercial rounds.

According to the official C.I.P. (Commission Internationale Permanente pour l'Epreuve des Armes Feu Portatives) guidelines the .308 Winchester case can handle up to 415 MPa (60,190 psi) piezo pressure. In C.I.P. regulated countries every rifle cartridge combo has to be proofed at 125% of this maximum C.I.P. pressure to certify for sale to consumers...............
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Old 10-31-2012, 02:32 PM   #12
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The problem in the 223 chambered rifles is the throat. It is longer in the 5.56. While it is only a 10% overload which is easily handled by most actions the shorter throat can cause a pressure surge to 30% or higher especially with the heavier bullets. Now as to the 308, I have fired surplus 7.62x51 in a 308 and had heavier recoil and mild signs of high pressure. The NATO round was hotter than the 308. I believe it was South African. I have never had an opportunity to fire 308 in a NATO chambered rifle.
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Old 10-31-2012, 02:32 PM   #13
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Quote:
Originally Posted by 303tom View Post
.223/5.56...........
According to the official Commission Internationale Permanente pour l'Epreuve des Armes Feu Portatives (C.I.P.) guidelines the .223 Remington case can handle up to 430 megapascals (62,366 psi) piezo pressure. In C.I.P. regulated countries every rifle cartridge combo has to be proofed at 125% of this maximum C.I.P. pressure to certify for sale to consumers. This is equal to the NATO maximum service pressure guideline for the 5.56x45mm NATO cartridge.

According to the official NATO proofing guidelines the 5.5645mm NATO case can handle up to 430 MPa (62,000 psi) piezo service pressure. In NATO regulated organizations every rifle cartridge combo has to be proofed at 125% of this maximum pressure to certify for service issue. This is equal to the C.I.P. maximum pressure guideline for the .223 Remington cartridge, that is the 5.5645mm NATO parent cartridge.

.308.7.62............
Although not identical, the 7.6251mm NATO and the commercial .308 Winchester cartridges are similar, and even though the Sporting Arms and Ammunition Manufacturers' Institute (SAAMI) considers it safe (by not listing it) to fire the NATO round in weapons chambered for the commercial round, there is significant discussion about compatible chamber and muzzle pressures between the two cartridges based on powder loads and wall thicknesses on the military vs. commercial rounds.

According to the official C.I.P. (Commission Internationale Permanente pour l'Epreuve des Armes Feu Portatives) guidelines the .308 Winchester case can handle up to 415 MPa (60,190 psi) piezo pressure. In C.I.P. regulated countries every rifle cartridge combo has to be proofed at 125% of this maximum C.I.P. pressure to certify for sale to consumers...............
The difference is in throating. 556 and 308win have longer throats than 223 and 762nato have shorter throats. When you load longer profile bullets into those chambers the pressure jumps radically to dangerous levels. The 762nato is chambered to use a 147grain bullet when you use larger ones in the 175grain and up the ogive can touch the lands. Thats why you dont use 308win in a nato chamber.
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Old 10-31-2012, 06:55 PM   #14
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If I am not mistaken I believe another difference is the method used to measure pressure is different for the american specs (.223, .308) than for the european specs (5.56, 7.62). This means the numbers are not an apples to apples comparison.
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Old 10-31-2012, 07:33 PM   #15
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I've had no problem shooting both 308 and 7.62X51 in my Bushmaster MOE 308 and according to Bushmaster it's fine.
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Old 10-31-2012, 09:33 PM   #16
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Quote:
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If I am not mistaken I believe another difference is the method used to measure pressure is different for the american specs (.223, .308) than for the european specs (5.56, 7.62). This means the numbers are not an apples to apples comparison.
Pressure in psi (Pounds per Square Inch) is the same no matter who measures it. Now if one were cup and one psi then yes. There is no formula to derive one from the other.

CUP = Copper Units of Pressure.
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Old 11-01-2012, 12:26 AM   #17
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Originally Posted by gunnut07 View Post
Pressure in psi (Pounds per Square Inch) is the same no matter who measures it. Now if one were cup and one psi then yes. There is no formula to derive one from the other.

CUP = Copper Units of Pressure.
The man has a point! The fomulas that try to change CUP to PSI, or visa versa just don't work.
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Old 11-01-2012, 12:31 AM   #18
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Quote:
Originally Posted by gunnut07 View Post
Pressure in psi (Pounds per Square Inch) is the same no matter who measures it. Now if one were cup and one psi then yes. There is no formula to derive one from the other.

CUP = Copper Units of Pressure.
WHO is not relevant to the measurement but WHERE is a very important factor.

http://guncentral.net/Articles/SAAMIvsNATO.html
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Test barrels made for 5.56 mm NATO measure chamber pressure at the case mouth, as opposed to the SAAMI location. This difference accounts for upwards of 20,000+ psi difference in pressure measurements. That means that advertised pressure of 58,000 psi for 5.56 mm NATO, is around 78,000 psi tested in .223 Rem test barrels (SAAMI .223 Rem Proof MAP is 78,500 psi so every 5.56 mm round fired is a proof load, very dangerous).
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Old 11-01-2012, 12:53 AM   #19
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I don't worry about it any more. I sold my .308 and bought a Remington Model 722 bolt action in .300 Savage. I love the older cartridges that everyone at the range does not have. I get sub-moa accuracy from this old rifle at near .308 velocities. I make brass for it from .308 brass, and it is very easy to do. Just an old fart having fun.
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