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Ballistic gelatin is a testing medium scientifically correlated to swine muscle tissue (which in turn is comparable to human muscle tissue), in which the effects of bullet wounds can be simulated. It was developed and improved by Martin Fackler and others in the field of wound ballistics. 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.
The most commonly used formula is a "10% ballistic gelatin", which 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 °C (39 °F). The older NATO formula 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 by Martin Fackler recommends that the water should not be heated above 40 °C (104 °F), as this can cause a significant change in the ballistic performance.
To ensure accurate results, immediately prior to use, the gelatin block is "calibrated" by firing a standard .177 caliber (4.5 mm) steel BB from an air gun over a gun 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 183 ± 3 m/s (600 ± 10 f/s), and a BB penetration between 8.3 and 9.5 cm (3.25 to 3.75 inches).
In his book Bullet Penetration, 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.
Ballistic gels made from natural gelatin are typically yellow-brown in color, and are not re-usable. Newer synthetic substitutes are engineered to closely simulate the ballistic properties of natural gelatin, while being colorless and crystal clear. Some synthetic gels are also re-usable, since they can be melted and reformed multiple times without affecting the ballistic properties of the gels.
Since ballistic gelatin mimics the properties of muscle tissue, as compared to porcine muscle tissues, 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 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.
In television the MythBusters team sometimes used ballistics gel to aid in busting myths, but not necessarily involving bullets, including the exploding implants myth, the deadly card throw, and the ceiling fan decapitation. They sometimes placed real bones (from humans or pigs) or synthetic bones in the gel to simulate bone breaks as well.
The US television program Deadliest Warrior is also known to use ballistics gel, often creating entire human torsos, complete with simulated bones and blood packs for organs and intestines cast inside the gel. Various weapons are then tested on the gel torso to simulate and record the destructive effects the weapons would have on a real human body.
- Fackerl, Martin L Effects of small arms on the human body. Letterman Army Institute of Research, California.
- Massad Ayoob (May/June, 2005) Backwoods Home Magazine. Wound Ballistics, Ballistic Injury, Stopping Power, Gunshot Wounds. Firearmstactical.com. Retrieved on 2012-08-14.
- Choose your ammo... police style: "This resulted in the FBI Wound Ballistics Workshop of 1988 in Quantico, Virginia. Among those present were Dr. Martin Fackler, head of wound ballistics research for the US Army’s medical training center, Letterman Institute. Fackler had developed an improved ballistic gelatin model that he had scientifically correlated to swine muscle tissue, which in turn is comparable to human muscle tissue. He hypothesized that wound depth was much more important than previously thought, and recommended ammunition that could send a bullet at least twelve inches into his ballistic gelatin."
- Fackler ML, Malinowski JA. (1988). "Ordnance gelatin for ballistic studies. Detrimental effect of excess heat used in gelatin preparation". Am J Forensic Med Pathol. 9 (3): 218–9. doi:10.1097/00000433-198809000-00008. PMID 3177350.
- Breeze, J. (12 January 2013). "Experimental penetration of fragment simulating projectiles into porcine tissues compared with simulants" (PDF). Journal of Forensic and Legal Medicine. 20: 296-299.
5^ Breeze, J., N. Hunt, I. Gibb, G. James, A. Hepper, and J. Clasper. "Experimental Penetration of Fragment Simulating Projectiles into Porcine Tissues Compared with Simulants." Journal of Forensic and Legal Medicine 20.4 (2013): 296-99. Web. 
- MacPherson, Duncan (1994). Bullet Penetration: Modeling the Dynamics and the Incapacitation Resulting from Wound Trauma. El Segundo, CA: Ballistic Publications. ISBN 0-9643577-0-4.
- Fackler ML, Malinowski JA. (September 1988). "Ordnance gelatin for ballistic studies. Detrimental effect of excess heat used in gelatin preparation". Am J Forensic Med Pathol. 9 (3): 218–9. doi:10.1097/00000433-198809000-00008. PMID 3177350.
- Jussila J. (2004-05-10). "Preparing ballistic gelatine—review and proposal for a standard method". Forensic Science International. 141 (2–3): 91–98. doi:10.1016/j.forsciint.2003.11.036. PMID 15062946.
- Putting Bullets to the Test, Officer.com
- 1998 INS testing procedure, detailing how ballistic gelatin is used to test service cartridges for a wide variety of situations.
- INLDT Report: Ballistic Gelatin, Penn State Applied Research Laboratory