The “Fackler” box is named for Dr. Martin Fackler, a wound ballistics professional whose work in his field has lead to the almost universal use of 10% gelatin to simulate flesh. Fackler experimented with several mediums. A Fackler box is simply a long, wooden box in which a row of plastic Zip-Loc bags full of water is placed. The bags are fired into from the test distance to obtain bullet penetration and expansion information.
For comparative purposes, water works fine, but the amount of bullet penetration you get in water will have to be measured in inches and multiplied by 0.56 to equal its penetration in gelatin. Water is a very hard medium for bullets and may tend to cause light, high velocity bullets to shatter.
I have used a Fackler box extensively for several years and have found that the number of bags needed to stop a bullet vary considerably. I’ve had as little as one bag stop an expanding .380 ACP, while it may take several feet of water-filled bags to stop a FMJ bullet fired from the same gun. As for rifles, a Fackler box is not a very practical way of recovering rifle bullets. My experience is that the hydraulic force created by the bullet entering the water at supersonic velocity almost always blows out the sides of the box.
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