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If you’re looking to install bullet proof glass, your first question is going to be “How do I know this will stop a bullet?”
The Role of Underwriters Laboratories (UL)
Stroll through your house and take a look at any gadget that could conceivable hurt you–the toaster, the TV, even the light sockets–and you’ll find a UL certification sticker indicating that the manufacturer submitted samples to Underwriters Laboratories, the nation’s leading third-party product safety certification agency. UL tests products to confirm that they fit within established safety specifications. In the case of bullet resistant barriers, that standard is UL 752, “The Standard of Safety for Bullet-Resisting Equipment.”
Bullet Proof Glass Rating Quirks
The chart is self-explanatory–provided that you know that “7.62mm” ammunition is used in an AK-47, “5.56mm” ammo in an M16, and that “.30 calibre rifle lead core soft point” basically means a hunting rifle–but it has its quirks. Levels 1 through 3 follow a reasonable sequence: A Level 1 system will stop three shots from a 9mm (arguably the world’s most common sidearm). Level 2 barriers stop three shots from a .357 Magnum–heavier ammunition moving at higher velocity. Level 3 barriers stop three .44 Magnum bullets (each of which is twice as heavy as a 9mm and moves significantly faster).
The Level 4 Challenge
To pass the Level 4 test, bullet proof glass must stop a shot from a .30-06 hunting rifle. This might seem easier than the Level 3 test, since it’s just a single bullet that’s lighter than the .44 Magnum. But, the .30 calibre is designed for penetration (important to hunters) and travels 1200 feet per second faster than the .44 Mag. The Level 4 test is actually harder to pass than Levels 5, 6, or 7. As Total Security Solutions vice president Jim Richards explains, that .30-06 bullet “is 180 grains of led moving at 2540 feet per second–you have a tremendous amount of velocity there with a big old piece of lead. Level 5 can be difficult, but still, it’s one shot of a 7.62 [just a touch heavier than a 9mm]; so it’s moving faster, but it’s a lot lighter.” A good Level 4 system can often pass the tests for Levels 5, 6, and 7 with little or no modification. That Level 4 system might even pass the Level 8 test (a five-shot burst from an AK-47). “It’s not guaranteed,” Jim is quick to point out, “but it’s pretty well established that if you can stop a .30-06, you’re set.”
The Curiously Organized Bullet Proof Ratings
Like many people in the bullet proof industry, Jim is genially perplexed by UL’s system. Practically speaking, Level 1 bullet proof glass–which will survive three shots form a 9mm–can often provide Level 6 and 7 protection, since Level 6 (the “Uzi test”) is a five-shot burst of that same 9mm ammunition, and most Level 1 systems will withstand more than the minimum three shots required to pass the Level 1 test. And, although the Level 7 (“M16”) test uses bullets traveling more than twice as fast as the Level 1 and Level 6 tests, those bullets are less than half the weight–M16 bullets are only slightly bigger than the .22s in a boy’s squirrel rifle. It’s the extremely high speed of these 5.56mm bullets that causes damage in the battlefield, largely through hydrostatic shock, an effect limited to living creatures.
This is the underlying rationale in the seemingly disorganized UL rating system: It’s not ordered according to the threat to materials, but rather the threat to the humans standing behind those materials. In practice, M16s and Uzis–with their fast, light rounds–aren’t very dangerous to a piece of bullet proof glass. But their fully automatic firing capacity is deadly: Battlefield and emergency room records confirm that when humans start shooting at humans, the propensity is to empty the clip. Conversely, the deer hunting rifle–despite its acrylic-shattering power–is an uncommon personal weapon: It’s a long-barreled rifle designed for accuracy over distance, and difficult to use in the close confines of a gas station or bank. And semi-automatic .30-06 rifles are rare, while the Uzis, M16s, and AK-47s used for the Level 5 through 8 tests are notorious for their lethal full-auto fire.