Ballistic gelatin

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Ballistic gelatin is a solution of gelatin powder in water. Ballistic gelatin closely simulates the density and viscosity of human and animal muscle tissue, and is used as a standardized medium for testing the terminal performance of firearms ammunition. While ballistic gelatin does not model the structure of the body, including skin and bones, it works fairly well as an approximation of tissue and provides similar performance for most ballistics testing. Ballistic gelatin is used rather than actual muscle tissue due to the ability to carefully control the properties of the gelatin, which allows consistent and reliable comparison of terminal ballistics.

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[edit] Preparation

The most commonly used formula, "10% ballistic gelatin", is prepared by dissolving 1 part 250 bloom gelatin into 9 parts of warm water (by mass), mixing the water while pouring in the powdered gelatin. It is chilled to 4° Celsius (39° Fahrenheit). An older formula used by NATO among others specifies a 20% solution, chilled to 10° C (50° F), but that solution costs more to prepare as it uses twice the amount of gelatin. In either case, a 1988 research paper[1] recommends that the water should not be heated above 40 C (104 F), as this can cause a significant change in the ballistic performance. For detailed preparation instructions, see [2] and [3].

To ensure accurate results, immediately prior to use, the gelatin block is "calibrated" by firing into it a standard .177 caliber (4.5 mm) steel BB, from an air gun over a chronograph into the gelatin, and the depth of penetration measured. While the exact calibration methods vary slightly, the calibration method used by the INS National Firearms Unit is fairly typical. It requires a velocity of 600 ± 10 f/s (183 ± 3 m/s), and a BB penetration between 3.25 and 3.75 inches (8.3 to 9.5 cm). 600 f/s is two to three times faster than the velocity of a BB propelled by a typical spring-air BB gun, and so where a typical BB gun might not penetrate the elastic skin of an animal, the higher velocity calibration shot will penetrate the gelatin more than might be expected.

In his book Bullet Penetration, (see [4]) ballistics expert Duncan MacPherson describes a method that can be used to compensate for ballistic gelatin that gives a BB penetration that is off by several centimeters (up to two inches) in either direction. MacPherson's Figure 5-2, Velocity Variation Correction to Measured BB Penetration Depth, can be used to make corrections to BB penetration depth when measured BB velocity is within ±10 m/s of 180 m/s. This method can also be used to compensate for error within the allowed tolerance, and normalize results of different tests, as it is standard practice to record the exact depth of the calibration BB's penetration.

[edit] Uses

Since ballistic gelatin mimics the properties of muscle tissue, it is the preferred medium for comparing the terminal performance of different expanding ammunition, such as hollow point and soft point bullets. These bullets use the hydraulic pressure of the tissue or gelatin to expand in diameter, limiting penetration and increasing the tissue damage along their path. While the Hague Convention restricts the use of such ammunition in warfare, it is commonly used by police and civilians in defensive weapons, as well as police sniper and hostage-rescue teams, where rapid disabling of the target and minimal risk of overpenetration are required to reduce collateral damage.

Bullets intended for hunting are also commonly tested in ballistic gelatin. A bullet intended for use hunting small vermin, such as prairie dogs, for example, needs to expand very quickly to have an effect before it exits the target, and must perform at higher velocities due to the use of lighter grain bullets in the cartridges. The same fast-expanding bullet used for prairie dogs would be considered inhumane for use on medium game animals like whitetail deer, where deeper penetration is needed to reach vital organs and assure a quick kill.

Forensic ballistics also uses ballistic gelatin in the recreation of wounds caused by firearms or explosives. For example, by comparing the depth of penetration in gelatin of a given bullet at different velocities, the approximate velocity at impact can be determined. This can then be compared to the expected muzzle velocity to determine how far the bullet traveled before it hit (see external ballistics), and thus can help determine the distance of the shooter.

Ballistics gelatin was introduced to the general population by the television shows MythBusters and CSI: Crime Scene Investigation, which show ballistic gelatin used in such a capacity. MythBusters uses ballistic gelatin for the widest range of purposes, testing not only bullets but also the lethality of pennies at terminal velocity and Kleenex boxes at highway speeds, and even electrocution. Their informal testing showed the gelatin provides a reasonable analogue to the conductivity and resistance of human tissue, and they used a ballistic gelatin dummy to determine if urinating on the third rail could concievably result in electrocution, to test if having tongue piercings increased the likelihood of being struck by lightning, and to find out if Benjamin Franklin would have survived having his famous experimental kite being struck by lightning, among other experiments.

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[edit] References

[edit] External links

How to make your own Ballistics Gelatin.

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