The heavy clothing test was developed by the FBI when that agency started testing ammunition in ballistic gel after the 1986 shootout where two agents died. It consists of four layers of clothing place in front of the gel block. The idea is to simulate clothing a person may be wearing and how that clothing may affect bullet performance.
Heavy clothing is often confused with the four layers of denim test developed by the International Wound Ballistics Association (IWBA). The FBI protocol calls for one layer of 14-ounce cotton denim, Polartec 200 fleece, 5.5 once cotton T-shirt, and 3.5-ounce cotton T-shirt. The IWBA protocol calls for four layers of cotton denim from 14.5 to 16 ounces.
As far as I know, the FBI has never used the four layers of denim in their testing. I have decided to use this standard in my testing instead of the four layers of denim. I personally think the four layers of denim to be a little unrealistic but I understand why some use it. Sometime, not often, I will use the four layer of denim if a bullet does well in the heavy clothing. I get my heavy clothing from Clear Ballistics simply for the convenience.
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