Glass is very hard on bullets, and it’s one of the more expensive portions of the test—a protocol that costs several thousand dollars.

The question often comes up, "You talk about the FBI tests, but exactly what are they?" As I mentioned in passing in my previous column, until the mid-1980s we did not have a scientifically repeatable tissue stimulant in which to test bullet performance. Then Dr. Martin Fackler--working at the U.S. Army Wound Ballistics Research Laboratory, Presidio of San Francisco--developed ballistic gelatin, which permitted researchers to test and compare bullet performance.

After the FBI Miami shootout--in which eight agents fought with two suspects, the latter continuing the battle even after being hit more than once--the Federal Bureau of Investigation set about creating a scientific method to measure bullet performance. I don't think the bureau intended to make the test an industry-wide standard, but that's the way things have turned out.

The process starts with gelatin, specifically Kind & Knox 250, in a 10 percent solution--one part gelatin by weight to nine parts water by weight. The process is strictly defined: The temperature during mixing has to remain within a limited range. If the mixing water is too hot or cool, then the strength of the resulting gel mix changes.

Once mixed, it is poured into molds and cooled. The mold size is defined for either handgun or rifle cartridge use. Handgun tests employ blocks that are 6x6x16 inches, and the blocks are cooled to 39.2 degrees and stored until needed.

The blocks must be shot within 20 minutes of being removed from the refrigerator. The gel blocks each have a thermometer stuck in them to check their temps. If they get too cool or warm, they are either adjusted or discarded.

Once the temperature is checked, then the block is further tested for consistency by having a steel BB fired into it. The BB is chronographed as it is fired, and if it is too slow or fast, the test has to be repeated. The pellet, once fired within an accepted range, has to penetrate a certain amount, plus or minus a small margin for error. Again, if it does not pass this test, the block is pitched.

FBI Ammo Test Video Watch a live FBI ammo test. Click Here

Finally, it has a bullet fired into it. One block, one bullet, 10 feet from muzzle to gel block. In some labs, the block can and will be melted, filtered, cast and re-chilled. In others, one use and it is gone.

Now we get to the interesting part: Repeat as necessary. You see, the FBI, in proper scientific fashion, shoots a number of bullets and then takes the averages of their performance: depth of penetration, expansion, retained weight, etc.

So five shots, each with its own block. Penetration is measured to the nearest quarter-inch, and expansion is measured as well. Expansion is the smallest diameter averaged with the largest diameter on each bullet.

But, wait, it gets better. The FBI recognizes that armed encounters rarely involve naked perpetrators. Bad guys do wear clothes, and they do hide behind things, so the bureau tests for those parameters, too. A full test will involve bare gelatin, as well as intermediate barriers of heavy clothing, plywood, auto glass, sheet metal and wallboard. And just to be thorough, the heavy clothing and auto glass tests are repeated at 20 yards in addition to the 10-foot distance.

The heavy clothing test uses four layers: T-shirt, dress shirt, synthetic insulation and heavy denim are laid against the face of the gel block before firing. The sheet metal test uses two six-inch square pieces of 20-gauge hot-rolled galvanized steel, set three inches apart and 18 inches from the gel block impact face. The gel also has a T-shirt layer on it.