Selecting a Ballistic Guard Shack – Part I: Bullet Resistance
December 3, 2009 at 08:00
What makes a guard booth “ballistic”? What one may visualize as a metal “box”, can actually be much more involved. Especially when it comes to a bullet resistant “box”, which is intended to be a potential live saving device. There are essentially two factors to consider when selecting a bullet resistance structure: Bullet Resistance and Points of Vulnerability. We’ll be focusing exclusively on bullet resistance in this post.
There are three main elements to consider when discussing the bullet resistance of armor:
Handgun vs. Rifle Protection
Unlike armoring for a vehicle or a person where weight can be an issue, when considering a bullet resistant structure it’s almost always better to over protect than under protect. The projectile velocity of a rifle is generally twice that of a handgun. To give you a general understanding, a standard 9mm full metal jacketed (FMJ), 124 grain, lead round fired from a common handgun has a muzzle velocity of approximately 1100-1400 feet per second (FPS). A standard .30 caliber (7.62 x 51mm), FMJ, 150 grain, lead core round fired from a .308 rifle has a muzzle velocity typically ranging from 2400-2800 FPS. In virtually all cases, the 7.62mm round will penetrate handgun armor as if it were not there at all.
In short, when choosing one level over another, it’s important to clearly understand just what it is you’re specifying. Make sure your armoring will protect you against any reasonable threat.
Not only should the handgun vs. rifle protection question be considered, but one should consider the types of ammunition that may be encountered.
With the abundance of ammunition types available today, this is a critical element when specifying your product. It’s simple (and common) to select your protection level based on an existing standard. For example, the National Institute of Justice (NIJ) or Underwriters Laboratories (UL). These are excellent standards and can be very effective. However, does this truly address all of the ballistic threats your environment may encounter? Probably not. A diligent security manager will determine what other threats exist and could realistically be encountered.
There’s nothing like getting a response from someone that starts with ”well, we took it out back and shot it with my buddy’s .22.” Over the years I have had countless groups approach me with a new material that “no one has”, that is “better and lighter” and “costs almost nothing to make”. When I inquire about threats and testing it usually starts with, “well we took it out behind the shop and…”
A ballistic test should be conducted in an independent, controlled environment by skilled technicians. There are several ballistic testing laboratories in the United States that do just this. The result is a test which validates that the armor meets the specified performance criteria set forth by the buying authority. These tests ensure that a specific ammunition type (including bullet weight and composition) is tested in accordance with the appropriate velocity and that the test sample is impacted at the proper “obliquity” (or angle of incidence), along with the number of impacts required over a specified surface area.
The most common criteria is to defeat the projectile at muzzle velocity (the velocity at which the projectile exits the barrel of the weapon) and 0-degree obliquity (otherwise defined as perpendicular to the plane tangent to the point of impact).
Lastly, when working with metallic armor there should be no exception to testing each individual Lot of armor that goes into the fabrication of your product. Not all armor is created equal. Just because one ½" armor plate defeats a certain projectile, it should in no way be assumed that all ½" plate will defeat it. Though it’s not common for Lots to vary, it can and does happen.
To sum it up, ensure your armor is rated to protect against any reasonable threat, including potentially uncommon threats. You should also require that armor is tested accordingly and that there is traceability from the steel mill to your end product, which includes mill certifications and ballistic testing of each Lot.
Stay tuned for part II of this series, where we discuss points of potential vulnerability in structural armor and how to reduce or eliminate those vulnerabilities.