Common Misunderstandings of Gel Tests
Guys, This is the second part of the last post about ballistic gel, again, I am reposting this from Red Dot Training range in PA. It may give you some direction on which carry ammo you use.
Myth 1: “Dramatic slow-motion gel tests show exactly what happens in a human body.”
Reality: Those high-speed videos of bullets hitting gelatin are fascinating and useful, but they can be misleading if taken as literal human wound profiles. The gelatin block often jumps and cavitates violently because it has uniform density and is not attached to anything. In a person, tissues are connected to a skeleton and supported by skin. They won’t jolt and rebound quite like a free block of gel.
The temporary cavity does correspond to stretching of tissues, which can contribute to wounding, but in human tissue many organs and blood vessels can stretch without rupturing immediately. Gel exaggerates the visible effect, whereas in reality a handgun bullet’s temporary cavity might cause subtle internal injuries that aren’t apparent externally.
So, while gel videos are useful to see how a bullet expands or fragments, one should not assume the magnitude of the gelatin’s reaction equals the damage done in a body. In fact, the FBI and wound ballistics experts emphasize that consistent penetration and bullet placement are more critical than any flashy explosion of gel.
The dramatic visuals are mostly a byproduct of the test medium being homogeneous and free to move. They demonstrate the bullet’s energy transfer, but a determined attacker might not be stopped unless a vital organ or CNS is hit, regardless of the temporary cavity size. In short, gel tests show relative performance (e.g. one bullet might create a larger temporary cavity or penetrate deeper than another in gel), but they do not show exactly what a wound in living tissue would look like.
Myth 2: “If a bullet penetrates X inches in gel, it will penetrate the same in a person.”
Reality: As discussed, gel penetration is a guideline, not a direct measure of inches in flesh. Twelve inches of gel ≠ twelve inches in a human. Bullets slow down or deform differently when encountering varying tissues.
For example, a bullet might penetrate 15″ in bare gel, but if that same bullet hits a human who is wearing heavy clothing and the bullet strikes a rib, it might only go, say, 9″ into the body, or could stop sooner if it loses energy shattering bone.
Conversely, if a bullet misses bones and travels through soft tissue, it might actually penetrate further than it did in gel. The FBI’s 12-18″ standard is intentionally conservative to account for these uncertainties. They wanted a bullet that at minimum can do 12″ in gel, believing this gives a good chance it will still reach vital organs through muscle, clothing, or intermediate barriers in a real shooting.
So, while the gel penetration number is very useful for comparing ammo, it’s not a precise prediction. Think of it like car crash tests: if a car’s safety cage holds up in a standardized crash test, it implies good protection, but real crashes vary. Similarly, 15″ of gel penetration suggests a robust bullet, but actual gunshot outcomes will depend on shot placement and target anatomy. Always interpret gel results as general indicators of performance rather than exact translations to real-world injury depth.
Myth 3: “Ballistic gel is supposed to simulate the entire human body.”
Reality: Gel is actually meant to simulate soft tissue (muscle) only. It deliberately does not include bone or complex organ structures, because those are much less uniform and harder to standardize.
The value of gelatin is that it’s the same everywhere. This lets testers isolate what the bullet itself is doing. If you introduced bones or varying tissues into the test medium, it would be more “realistic” in one specific scenario but far less consistent across different tests.
The FBI protocol addresses variability by adding separate barrier tests (like shooting through glass or plywood into gel) to see how bullets perform after defeating those obstacles. But the core measurement is still done in gelatin to keep things controlled. Everyone understands a bullet will behave differently in a human body (where it might glance off a bone or yaw unexpectedly), but by examining performance in gel, you get a baseline for penetration and expansion without those extra variables.
In summary, ballistic gelatin is a comparative tool, not a full-blown anatomical model. It’s the standard medium so that testers around the world speak the same language when they say, for example, “this 9mm penetrated 15″ and expanded to 0.60″ diameter through heavy clothing in gel.” That way, both law enforcement and civilians can make informed choices knowing those figures come from a consistent test medium.
Service Calibers and FBI Performance Standards
One major outcome of the FBI’s gelatin testing standards has been the levelling of the playing field among common defensive handgun calibers. In the past, there were heated debates about 9mm vs .45 ACP “stopping power,” or whether .40 S&W was superior, etc.
Today, thanks to modern bullet design, the truth is that all mainstream service calibers can be effective, because they’re all engineered to meet the same FBI performance criteria.
Whether it’s .380 ACP, 9×19mm, .40 S&W, or .45 ACP, the premium defensive hollow-point loads in these calibers are typically designed to penetrate roughly 12-18″ in gel and expand reliably along the way.
This means that when you use quality ammunition, a .40 S&W and a 9mm will both likely penetrate to a similar depth in gelatin and cause a similar size wound cavity.
The differences in real-world terminal effect between these calibers become much smaller than many people assume, provided the bullets perform as intended.
For instance, data has shown a modern 147 gr 9mm JHP can expand to about the same diameter and penetrate as far as a 180 gr .40 S&W JHP, because both are built to hit that FBI sweet spot.
A .45 ACP might start a bit larger in diameter, but its bullet is slower; a 9mm is smaller but faster. In the end, both can be made to penetrate ~14″ and expand, achieving very comparable results in gel tests. Even the .380 ACP, historically seen as marginal, has benefited from advanced bullet designs. While .380 is on the lower end of accepted performance, some newer .380 JHP loads do meet the 12″ minimum in gel (often by sacrificing some expansion for penetration). The FBI’s testing pushed manufacturers to improve even these small calibers.
What this means for both law enforcement and civilians is that shot placement and bullet choice are usually more important than caliber.
A well-designed 9mm bullet that meets the standard will perform as required, just as a well-designed .45 will. Neither is a magic “one-shot stopper” if it doesn’t hit something vital, and both are adequate if they do.
In law enforcement, many agencies moved back to 9mm because it offers higher capacity and easier recoil management while still meeting the FBI gel performance.
For civilian self-defense, the takeaway is to choose a reliable, tested defensive load in whatever caliber you carry. Don’t rely on caliber myths; instead, look at the gel-tested performance.
You’ll find that reputable defensive ammo across 9mm/.40/.45 is converging toward a similar level of penetration and expansion. All are trying to thread the needle: expand enough to cause damage and not over-penetrate, yet penetrate deep enough to reach crucial organs.
In the controlled environment of gel, they often perform very similarly within that FBI benchmark range. This highlights that handgun effectiveness is relatively limited no matter the caliber, a fact the gel tests underscore, and why shot placement, and multiple hits can matter more than a few millimeters of bullet diameter.
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