5.56 / .223 brass difference?

[bigedp51]

Since you guys are having this contest anyway, I thought I'd mention that:

1) NATO EPVAT, though it uses the same max pressure number as CIP, measures pressure in a different place than CIP (case mouth for NATO vs. 25mm forward of the case head for CIP), which means that at any given nominal reported pressure, the NATO measurement location translates to slightly higher chamber pressure than CIP's method (or SAAMI's, which measures in essentially the same place as CIP).

2) The US Army used psi 'forever' in reporting pressure figures obtained using copper crusher equipment. In the late '60s when it was finally universally accepted that copper crushers don't measure pressures quite the same (nor as accurately) as piezo transducers, SAAMI instituted "C.U.P." as a unit of pressure measurement. The military changed over, too, but what they reported in 'psi' for most of the 20th Century was in fact CUP, and the two are not the same.

3) That nifty pressure differential chart shows more rifle-to-rifle variation than it shows variation between the 2 types of ammunition.

Okay, that's all I have. Carry on with your contest. :)

Dear Contestant AKA MZ5

NATO EPVAT testing is the exact same testing method that the European CIP uses and are one in the same and both pressures are measured at the case mouth. This means in Europe military and civilian testing standards are the same BUT the Europeans do NOT use American SAAMI chamber pressure standards and methods.

When asked about pressures in a earlier posting I listed SAAMI 52,000 cup, SAAMI tranducer 55,000 psi and European CIP (NATO EPVAT) 62,000 psi. These three pressures are the exact same pressure measured by different means and standards. I listed these pressure so our different age groups would understand depending on which method they grew up with.

TM 43-0001-27 leaves many questions about M193 and M855 rounds chamber pressures, meaning is one of the pressures listed as a typo or are both pressures in CUP.

CARTRIDGE, 5.56MM, BALL, M193 Chamber pressure...............52,000 psi
CARTRIDGE, 5.56MM, BALL, M855 Chamber pressure ..............55,000 psi

Second, traditionally military cartridge cases were made thicker and heavier to withstand larger diameter chambers and longer headspaced chambers than their civilian counterparts.

During the testing phase of the M16 standard thickness commercial cartridge cases were used and problems arose with jamming and case head separations. Due to the small case capacity and Remington/DuPont inability to make IMR powder to military pressure and velocity standards a higher standard of brass was used and not diminish internal case capacity.

And the ball powder used in the M16 that caused the jamming problem was the same exact powder used in the M14 rifle and it was used because of its loading density.

Thank you MZ5 for being a contestant.
That nifty pressure differential you referred to was taken with a strain gauge glued to the barrel and used a commercial cartridge as a pressure reference calibration point.

Also, I use a tire pressure gauge calibrated in psi, it doesn't give pressures in cup or some silly European metric equivalent.
Have a nice day. :-)