Like Rost, I come from a highpower background, and in the early days of the AR15 Service Rifle, WW748 was attractive because it showed very good velocities even with the heavy bullets that we were using. The reality like Rost says is that it's a psychotic powder with temps. What was safe when you worked it up in 60 degree temps might blow primers in the summer heat of Camp Perry.
Here's some info regarding 223 pressures vs 5.56 pressures off of Wikipedia;
"NATO EPVAT test barrels made for 5.56 mm NATO measure chamber pressure at the case mouth, as opposed to the location used by the United States civil standards organization SAAMI. The piezoelectric sensors or transducers NATO and SAAMI use to conduct the actual pressure measurements also differ. This difference in measurement method accounts for upwards of 137.9 MPa (20,000 psi) difference in pressure measurements. This means the NATO EPVAT maximum service pressure of 430 MPa (62,366 psi) for 5.56 mm NATO, is reduced by SAAMI to 379.21 MPa (55,000 psi) for .223 Remington.[12] In contrast to SAAMI, the other main civil standards organization C.I.P. defines the maximum service and proof test pressures of the .223 Remington cartridge equal to the 5.56 mm NATO."
I AM set up to run strain pressures on my AR, and I've run pressures on factory 223 as well as USGI M855. I kept scratching my head on why the M855 was no hotter than a lot of the factory 223 I ran. I'd heard that NATO pressures were higher. Rost kept telling me to give him the 60K data. I'd heard the measurement protocols were different. That article was the best explaination of how and why.
Oh yeah...SAAMI max on a 223 is 55K...not 50K or 52K, and contrary to what is out there on the internet...while it certainly holds true for 7.62, most LC 5.56 and other USGI 5.56 brass is not heavier with less internal capacity than commercial brass.
Last edited by ChrisF; 10/29/09.
