All sizes in millimeters (mm). The rifling twist rate for this cartridge is 177.8 mm (1 in 7 in), 6 grooves right hand twist, Ø lands = , Ø grooves = . According to STANAG 4172 and the official NATO proofing guidelines the 5.56×45mm NATO case can handle up to piezo service pressure. In NATO regulated organizations every rifle cartridge combination has to be proofed at to certify for service issue. STANAG 4172 defines the Belgian ball cartridge SS109 as the NATO reference cartridge and adds a considerable number of technical requirements like a minimum pressure of at the gas port down the long standard proof barrel and primer sensitivity that are not defined by civilian C.I.P. and SAAMI ammunition rulings and recommendations. The NATO military alliance uses a NATO-specific recognized class of procedures to control the safety and quality of firearms ammunition called NATO EPVAT testing. The civilian organisations C.I.P. and SAAMI use less comprehensive test procedures than NATO. The NATO Manual of Proof and Inspection AC/225 (LG/3-SG/1) D/8 stipulates each weapon and component considered vulnerable to the effects of a rapid change in pressure, for example barrels, breech blocks and bolts, will be tested by firing one dry round at a corrected minimum of 25% over pressure and one oiled round at a corrected minimum of 25% over pressure. Over pressure of 25% means 25% in excess of the service pressure resulting for the 5.56×45mm NATO up to (Pmax) piezo service pressure. The service pressure is defined as the mean pressure generated by the service cartridge at a temperature of . Such a high pressure proof is conducted with both the weapon and ammunition conditioned to an ambient temperature of . Each weapon will be individually tested, from an ammunition lot that produces a minimum corrected mean chamber pressure. The corrected proof pressure requirement (service pressure (Pmax) + 25%) for the 5.56×45mm NATO like the STANAG 4172 is (PE) piezo pressure. This pressure has to be recorded in a NATO-design EPVAT barrel with Kistler 6215 transducer, HPI GP6 Transducer or by equipment to C.I.P. requirements. The US SAAMI lists maximum average pressure (MAP) for the .223 Remington cartridge as piezo pressure with deviation of up to . Rifle barrel configurations When 5.56×45mm NATO was adopted as standard in 1980, NATO chose a 178 mm (1:7) rifling twist rate for the 5.56×45mm NATO chambering to adequately stabilize the relatively