by at least 10 percent, as well as for the 7.62 NATO and .50 BMG rounds. The cartridge cases must maintain all performance requirements when fully assembled, be able to be used by the Lake City Army Ammunition Plant, must be manufactured in quantities totaling approximately 45 million per year. Polymer-cased ammunition is expected as a likely lightweight case technology. A hybrid polymer/metal version of a conventional cartridge case would be thicker than regular cases and reduce the amount of space for the propellant, although certain polymers could be thermodynamically more efficient and not lose energy to the case or chamber when fired. Pressure C.I.P. defines the maximum service and proof test pressures of the .223 Remington cartridge equal to the 5.56mm NATO, at . This differs from the SAAMI maximum pressure specification for .223 Remington of , due to CIP test protocols measuring pressure using a drilled case, rather than an intact case with a conformal piston, along with other differences. NATO uses NATO EPVAT pressure test protocols for their small arms ammunition specifications. Differences in testing methodology have led to widespread confusion, however when measured with identical measuring equipment using identical methodologies, .223 Remington yields peak average pressures about 5,000 psi lower than 5.56 NATO. Chamber The 5.56mm NATO chamber, known as a NATO or mil-spec chamber, has a longer leade, which is the distance between the mouth of the cartridge and the point at which the rifling engages the bullet. The .223 Remington chamber, known as SAAMI chamber, is allowed to have a shorter leade, and is only required to be proof tested to the lower SAAMI chamber pressure. To address these issues, various proprietary chambers exist, such as the Wylde chamber (Rock River Arms) or the ArmaLite chamber, which are designed to handle both 5.56×45mm NATO and .223 Remington equally well. The leade of the .223 Remington minimum C.I.P. chamber also differs from the 5.56mm NATO chamber specification. The casings and chambers .223 Remington and 5.56×45mm NATO are virtually the same dimensions, but due to the fact that .223 Remington is designed to handle much lower pressures than the 5.56×45mm NATO the rounds are not completely interchangeable. Firing a 5.56×45mm NATO round out of a rifle chambered in .223 Remington could be injurious or fatal to the user as well as the gun, however .223 Remington ammunition can be fired safely from almost any rifle chambered