As the base of the case is not supported by the chamber, excess pressure inside the case will cause this area to expand directly proportionately with the amount of excess pressure present. As pressure curves for production ammo go, these ten shots of Federal 5.56 ammo in an FNH-USA 5.56MM chamber were relatively consistent. There will be ample evidence to confirm the existence of dangerous pressure levels directly attributable to the overlength cases: The shooter may get belted sorely in the … If the primer pocket expands too much, it will be too large to hold a primer. To correct the calculation for the consistent temperature, volume, and /or virtual leak changes that occur during the test cycle, there is a “tare” factor that offsets the pressure … The pressures SAAMI is concerned with are exclusively chamber, not down-barrel pressures. Trying to push your reload any stronger exceeds the design limits of the ammunition components and gun. There is a reason why this is called a MAX load – because it is! The MAX load pressures shown by Hodgdon match the industry standards, just as the ammunition loading companies do in factory loads. 03-09-2010, 06:47 AM. Cylinder pressure for R&D work, optimized for precision of measurement. Since the pumping speed is now zero, any gas entering the chamber will be accumulated. Cylinder pressure measurements play the key role in any engine indicating and combustion analysis work, but since modern engine research requires more than peak cylinder pressure to be measured against crank angle, pressure transducers are also made for the following roles in engine indicating work:. Chamber pressure has no direct correlation to port pressure. These curves are often referred to as “leak-up curves” or “leak-up rate.” Of course, make sure you use the appropriate powder to keep the pressure curve within spec. Chamber pressures in this situation can and most certainly will go dangerously high [Fig. When the vent is opened, air at atmospheric pressure flows into the chamber at no greater than sonic velocity, no matter how low the pressure is inside the chamber. The observed chamber pressure for Federal XM855 5.56mm ammunition in a .223 Rem chamber exceeded .223 maximum pressures, but not by a massive amount. Port pressure is what exists at the gas-port location within the barrel bore. As venting continues and the chamber fills with gas, the pressure inside the chamber rises until it reaches P ATM x 0.528, or 528 mbar (7.76 psi). Chamber pressure and port pressure are two different animals. milboltnut.   Back to home. process to completely stop, there will be a small and fairly consistent pressure loss associated with a non-leaking master part. The M1 is far stronger than that from the standpoint of blowing up, but that isn't the point of a proof load. 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