The NIJ ballistic resistance standard classifies body armor by levels of ballistic performance. For any performance level, NIJ’s test protocol requires that the bullet does not perforate the vest and that the vest protects against blunt trauma.
NIJ LEVEL IIIA (.44 Magnum; Submachine Gun 9mm):
This armor protects against .44 Magnum, Semi Jacketed Hollow Point (SJHP) bullets with nominal masses of 15.55 g (240 gr.) impacting at a velocity of 426 m/s (1,400 ft/s) or less and against 9mm full-metal jacketed bullets with nominal masses of 8.0 g (124 gr.) impacting at a velocity of 426 m/s (1,400 ft/s) or less. It also provides protection against most handgun threats as well as the Level I, IIA, and II threats. Level IIIA body armor provides the highest level of protection currently available from concealable body armor and is generally suitable for routine wear in many situations. However, departments located in hot, humid climates may need to evaluate the use of Level IIIA armor carefully.
NIJ LEVEL III (High-powered rifle):
This armor, normally of hard or semirigid construction, protects against 7.62mm full-metal jacketed bullets (US military designation M80) with nominal masses of 9.7 g (150 gr.) impacting at a velocity of 838 m/s (2,750 ft/s) or less. It also provides protection against threats such as 223 Remington (5.56mm FMJ), 30 Carbine FMJ, and 12-gauge rifled slug, as well as Level I through IIIA threats. Level III body armor is clearly intended only for tactical situations when the threat warrants such protection, such as barricade confrontations involving sporting rifles.
NIJ LEVEL IV (Armor-piercing rifle):
This armor protects against .30–06 caliber armor-piercing bullets (US military designation APM2) with nominal masses of 10.8 g (166 gr.) impacting at a velocity of 868 m/s (2,850 ft/s) or less. It also provides at least single-hit protection against the Level I through III threats.
Level IV body armor provides the highest level of protection currently available. Because this armor is intended to resist “armor piercing” bullets, it often uses ceramic materials. Such materials are brittle in nature and may provide only single-shot protection since the ceramic tends to break up when struck. As with Level III armor, Level IV armor is clearly intended only for tactical situations when the threat warrants such protection.
More information on ballistic-resistant body armor classifications and testing protocols can be found at NIJ STANDARD–0101.06.