There is a lot of misconception out there about ballistic gel, which leads to some pretty bad conclusions about defense ammo. One of the more popular mistakes is the claim that ballistic gel is not an exact simulation of tissue. Paradoxically, this one is a little sticky because taken at face value, that’s actually correct. It isn’t a perfect simulation, but for that matter, actual living bodies are not a perfect prediction of what will happen in a shooting because every body is different, the exact angle of impact will vary, the tangent of the bullet to a round bone is literally infinitely variable, and many more significant variables are simply impossible to control. But properly prepared and calibrated 10% ordnance gelatin does produce penetration, retained weight, and expansion/fragmentation results that correlate very strongly with wounds observed in actual bodies. It is near perfect for simulating those measurements in living muscle tissue and the results in other soft tissues do not tend to deviate significantly. It is also homogenous and easily reproducible so variables can be controlled and results compared.
As a measure of what a projectile can do in soft tissue, it’s quite close, but that’s not quite what it is intended for. We aren’t meant to overlay an image of a gel block on a human torso and conclude that the damage will be exactly as seen in the block. That bone that I mentioned a moment ago tends to significantly affect performance. Bone usually fragments and bullets that strike bone can also fragment. Fragments from both tend to be low mass and penetrate shallowly but substantially increase bleeding near the impact. Bone can also prevent expansion for a JHP and it can deflect bullets from their original path.
The purpose of using ballistic gel is to compare one load to another in relative terms. We can see that two bullets penetrate about the same but if one expands more, it can obviously damage a bit more tissue. Or we can conclude that a bullet that fails to meet the 12″ penetration standard is likely to be less effective than one that performs similarly but exceeds the 12″ mark.
Where we see a lot of confusion, though, is when informal testers misinterpret gel results by believing that disruption seen in the gel is representative of wounding. Natural, collagen based 10% ballistic gelatin is much less elastic than real tissue and will tear easily. The tears seen in the gel block are roughly indicative of the general size of the temporary stretch cavity and can give an indication as to how early a bullet began to expand, yaw, or fragment. But real tissue (with the exception of brain, liver, and spleen) tends to stretch much farther without tearing. There is some disagreement among the experts, but a 2,000 fps impact velocity is often held as the threshold where the temporary stretch cavity becomes large enough to contribute to wounding through tearing. ClearBallistics clear gel is much more elastic than real gelatin or muscle tissue, but it will tear easier than muscle. If that sounds contradictory, consider that you can pull clear gel farther apart without tearing it, but it takes less effort to cause a tear. Kind of like how plastic wrap is both more elastic and easier to tear than a beer can. If you were to take a pork roast and try to push your finger into it, you basically could not cause your finger to perforate the meat unless you were very strong. I know that I can’t. But I can poke my finger into natural ballistic gelatin relatively easily and I can poke it into clear gel with a bit more effort. I can take a hunk of clear gel and tear it apart with my hands, but I would have great difficulty in getting meat to do that, except where it might separate along the various muscle groups.
The reason this distinction is important is that, when amateur testers point to disruption in a block as proof that ammunition is effective, they are flatly incorrect. Disruption seen in gel is a result of cutting or tearing and it does not correlate well with cutting or tearing that happens to real tissue from the same ammunition. That disruption might look cool, but it is not representative of anything that occurs in tissue. So when you see those videos reviewing the next gimmicky death blaster screw driver ammo, understand that the only results that the gel can give you that are actually relevant are penetration, expansion/fragmentation, and retained weight. If they make the claim that the disruption in the gel equates to “wounding” “permanent cavity” or anything similar, you may safely conclude that they really don’t know what they’re talking about. Their measurements may be accurate, but their opinion about the effectiveness of the ammo might not be.