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Old 12-03-2012, 4:43 PM
ptmn ptmn is offline
Join Date: Aug 2012
Location: SF Bay Area
Posts: 481
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One of the reasons why you are getting more velocity out of M193 is because it is loaded to higher pressure than the .223 load data that you are pulling from your reloading manual. Higher pressure of the military loading equals higher velocity. I have an excerpt from an article regardign the pressure difference between SAAMI vs Military M193 loadings:
The 5.56 mm NATO and .223 Remington cartridges and chamberings are similar but not identical. Military 5.5645mm cases are often made thicker and therefore have less case capacity.[26] However, the NATO specification allows a higher chamber pressure. 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 20,000 psi (140 MPa) difference in pressure measurements. This means the NATO EPVAT maximum service pressure of 430 MPa (62,000 psi) for 5.56 mm NATO, is reduced by SAAMI to 55,000 psi (380 MPa) for .223 Remington.[27] 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.
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