How Penetration and Section Density Affect Terminal Performance


All handgun charges were fired in an arranged stack of 2 x 6 inch treated pine planks

Penetration is a critical aspect of terminal performance. As the great African hunter and professional writer Finn Aagaard once wrote: “The power to kill is a matter of biology, not math and physics, and is almost totally influenced by the placement of shots, accompanied by a sufficient penetration. The Federal Bureau of Investigation (FBI) agrees; he defined 12 inches of penetration as sufficient depth when ammunition is tested in 10 percent ammo gelatin. The Bureau also exposes bullets to a variety of intermediate barriers such as automotive glass, steel, plywood, and wall panels.

Ten percent gelatin and similar media are great for testing terminal performance. They provide an indication of the penetration potential and allow estimation of expansion and soft tissue damage. However, software test stands are impractical for the most penetrating loads, as it is almost impossible to arrange enough test blocks in a line long enough to stop bullets. Additionally, bullets that can penetrate more than 3 feet into a 10 percent artillery gelatin often deflect just enough to exit the side of a 6 inch wide test block before penetration is complete.

I recently received new 147 grain 9mm ammunition from Federal from its Solid Core range. This ammunition uses an extremely hard lead bullet with a high antimony content, commonly known as a hardened bullet. However, Federal Solid Core loads are a little different as the balls are coated with the Syntech polymer sheath material to reduce friction and advance. With traditional hard cast charges, this is most often accomplished with wax rings and gas controls. Federal Solid Core ammunition is intended for predator defense and big game hunting, and in addition to the existing 9mm charges, .40 S&W, 10mm and .45 ACP are expected to be available soon.

I wanted to see how deep this 147 grain 9mm load would penetrate compared to more common loads. But, I didn’t want to try to line up five or six blocks of gelatin to try to stop the ball. My answer was, as my grandfather would have said, “simple mountaineer”. I stacked one foot sections of a 2 x 6 inch treated pine board and clamped them together. Then from 10 feet I pulled the new Federal Solid Core 9mm load and eight other loads into the wood blocks. I’m not saying it was a highly scientific experiment, but rather an interesting proof of concept.

The first bullet recovered was the 135 grain .45 ACP Honey Badger charge; it only partially penetrated the third plank. The two 230 grain .45 ACP bullets – the FMJ and the Hydra-Shok – entered the third plank, but did not exit. The Honey Badger 100 grain 9mm did the same. The Federal HST 9mm 124 grain, FMJ 147 grain, and Syntech 147 grain bullets all entered the fourth plank, but did not exit. The last two bales, a 130 grain load for the .327 Fed. Mag. Buffalo Bore and the Federal 9mm Solid Care 147 grain filler has been incorporated into the fifth plank.

You might be wondering why the two notorious self-defense bullets, the Hydra-Shok and the HST, failed to develop. After all, the two do well on the FBI’s plywood barrier test; they penetrate the plywood and then expand upon impact on the 10 percent gelatin block. Well, for starters, that’s precisely what these bullets were designed for. With the plywood barrier test, the ball should only pass through one piece of 0.75 inch plywood. The ball is not exposed to enough compressible wood to fill the nasal cavity and prevent the essentially incompressible gelatin, which is 90% water, from blooming these balls in their usual recovered form. In the pine boards, the hollow points of these balls were filled with wood – wood much softer than the balls and which was tightly compressed into the hollow point. Without introducing an incompressible liquid into the hollow point cavity, expansion was avoided.

Projectiles recovered from the pine planks showed little deformation. The penetration depth corresponds to the speed and the section density.

While the shape of the ball plays a small role, just as a more aerodynamic ball glides more easily through the air, in my experience, penetration was primarily a product of speed and section density (SD). Bullets with the best combination of speed and SD penetrated the deepest. But, when expanding bullets like HST and Hydra-Shok are fired into soft tissue as in FBI tests, the section density of the unfired bullet cannot be taken as an indicator of the potential for penetration. . This is because the weight of the bullet relative to its diameter – its section density – changes immediately after impact.

For example, an undrawn 9mm 124 grain HST bullet has an SD of 0.140, but after penetrating an inch into 10 percent gelatin or soft tissue and expanding to about 0.6 inch in diameter, its SD is closer to 0.055. That is why in soft tissue, the HST load will only penetrate about 14 inches, but an FMJ load with the same SD will push up to three times deeper.

Test results

Now, unless you find yourself in a lumberyard shootout or have a shootout while building a bridge at the back of your abode, it’s doubtful that it has a practical connection to the use of a handgun to defend against a human attacker. On the other hand, if you’re worried about having to shoot through hard or thick barriers, or stopping a charging grizzly, take note. Some bullets can do it, some can’t.

Either way, it’s clear that Federal’s new 9mm Solid Core filler is an extremely deep penetration option for the 9mm. It will exceed common FMJ loads and extend 9mm and 0.45 ACP. It should also effortlessly shoot any villain, no matter how small, while still providing sufficient penetration on a cougar, bear, or even a menacing saber-toothed tiger. Of course, don’t forget the other half of Aagaard’s “kill power” tip: Not all penetration in the world will make up for a bad shot.

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