Just a little history to go with this old thread. As has been noted in a previous post, 4 layers of Denim was never an FBI standard. So where did it come from? It was promulgated by the now-defunct International Wound Ballistics Association (IWBA), and was chaired by Dr. Martin Fackler. Fackler was a military physician and was the chief proponent of gelatin testing. He was a big believer in deep penetration, and having come from a military setting, he didn't think there was any such thing as over-penetration, and completely discounted expansion.
At the time, many hollow point bullets expanded well in various media such as water jugs, wet newspaper, and even modeling clay, which were all used by amateur testers. But when those same bullets encountered some intermediate barrier, they often clogged and failed to expand in the real world. The 4 layers of denim test was specifically designed to make hollow points of the day fail to expand. The theory was that if a bullet got past the denim and still expanded, it was likely to work well in a variety of situations. This test has become the darling of backyard testers because it is easy to set up (sort of, using some old jeans), but it bears no relation to FBI tests that are used by government agencies or ammunition manufacturers.
The test is actually harder on a bullet than the real FBI Heavy Clothing Test, which is designed to simulate real world clothing. Quite a few rounds do well on FBI Heavy Clothing that don't look good through 4 layers of denim. Again, its original purpose was to make a hollow point fail. The old FBI load, especially from a 2-inch, is one such load.
As for the original FBI style LSWCHP +P, I've had occasion to see a couple dozen of them pulled out of human bodies on autopsy and from surgery fired from a mix of 2-inch and 4-inch guns used with the Winchester load by our city police department in the 70's and 80's. On a good torso hit, we'd usually find them under the skin of the back of the shot person, not classically expanded, but usually deformed and looking like a piece of parking lot gravel. It was about even money on whether the person would be dead or not, but the reputation among our cops was that if you could shoot well (and that was easy in a steel K-frame with this load), one or two hits were going to settle matters. I know that when we switched to the SIG P226 loaded with very early 147 grain 9mm loads, there was a feeling that the new gun held more shots, but didn't work as well. A move to the 124 +P Hydra Shok round fixed that right up.
I carried the city issued load in an Airweight J-frame off duty for a while when I was young and thought recoil was fun, and because we could get it for free. I never had any doubts that the load would do its job if I did mine. But I liked it a lot better in our issued Model 64's.
