More on 7.62 NATO Pressure

[green]

I recently purchased " More on the Fabled FAL", Stevens, and its new material on the pierced primer scare with the C1 rifle. Lot DAQ 210 of 7.62 NATO ammo which produced the pierced primers gave 73900 psi pressure which was high vs 61000 psi of lot DAQ 142 which was acceptable.
Not to get into the debate over 7.62 vs .308" Winch it appears that the 7.62 round is in no way a reduced load vs the .308".

 

[Lee Enfield]

Picked the book up right when it came out. A little new info about the CAL tool room guns.

The thing about the pressure levels which most people don't understand is that you just can't compare numbers, you have to ensure that the methods of testing are the same.

for example from SAAMI publication Z.299.4 1992

"Service" Transducer Maximum Average Pressure (MAP):
.308 62,000PSI
"Definitive Proof" Transducer Maximum Average Pressure (MAP):
.308 min: 83,000PSI
.308 max 89,000PSI

"Service" Crusher (CUP) Maximum Average Pressure (MAP):
.308 52,000PSI (CUP)
"Definitive Proof" Crusher (CUP) Maximum Average Pressure (MAP):
.308 min: 69,500PSI (CUP)
.308 max: 74,500PSI (CUP)

That's 2 systems of measuring the exact same pressures, notice the differences?

Then is that the .308 Maximum Average Pressure (MAP) (62,000 PSI/52,000 CUP), Maximum Probable Lot Mean (MPLM) (63,600 PSI/53,300 CUP), or Maximum Probable Sample Mean (MPSM) (66,000 PSI/55,300 CUP).

Notice that both the MPLM and MPSM are higher than the "Service" MAP for .308....and yet still acceptable.

Which units are referred to in "Fabled FAL"? Does the 1950's NATO method of pressure testing resemble the SAAMI one?

 

[tjhaile]

The current NATO pressure test standard uses a transducer, albeit with a different procedure from SAAMI tests.

http://en.wikipedia.org/wiki/NATO_EPVAT_testing

The belief that there is a significant pressure difference between .308 and 7.62x51 comes from confusion between copper crusher and transducer pressure numbers. US Army TM-43-0001-27 gives a pressure for 7.62 NATO of 50,000 psi, which would appear to be by the copper crusher method, given the NATO transducer pressure in the above article.

 

[Lee Enfield]

The current NATO pressure test standard uses a transducer, albeit with a different procedure from SAAMI tests.

http://en.wikipedia.org/wiki/NATO_EPVAT_testing

The belief that there is a significant pressure difference between .308 and 7.62x51 comes from confusion between copper crusher and transducer pressure numbers. US Army TM-43-0001-27 gives a pressure for 7.62 NATO of 50,000 psi, which would appear to be by the copper crusher method, given the NATO transducer pressure in the above article.

A large part of the NATO standards are brass case and rim hardness and deformation consistancy, mostly aimed at ensuring consistant functioning in a large variety of automatic weapons.

 

[Ganderite]

I have had the opportunity/job of pressure testing both SAAMI and NATO ammo.

The limits for 308 and 7.62 are about the same. The difference is not worth noticing. Both flavours run in the 55,000 to 60,000 psi range, with hot lots of both running up to 62,000 average.

The original published specs for NATO were CUP numbers, but the NATO documents referred to the limits as "psi", not "CUP" as is the custom. This caused (es) the confusion.

Here is a test that included both SAAMI (Norma) and some Lake City (NATO).