July 21, 2020
There have been many different methods and mediums used over the years to measure ammunition performance and predict results on flesh. Shooting hanging cadavers, baffle boxes of spaced pine boards, wax, clay, Duxseal, phone books (both wet and dry), wet newspapers, 20% gelatin and now 10% gelatin. All are methods that allow you to compare performance of one fired projectile to another, so you can determine the best caliber or the best bullet for your intended application. The ultimate goal of all was to measure the performance and be able to accurately predict effectiveness on live tissue. This would enable you to select one projectile or ammunition type as being more effective than other types.
The space allotted for this article will not allow a detailed comparison of each of the mediums I mentioned, with an assessment of the strong points of each. For now, I can simply state that 10% gelatin is the most universally recognized method of simulating performance against live tissue.
Ballistic gelatin testing basically involves molding blocks of gelatin, shooting the blocks and measuring the damage you create. The gelatin blocks are literally Jell-O. They are made of Knox gelatin similar to what your mother fed you as a kid, but without flavoring and made to a denser consistency. A typical 8x8x17 inch block of gelatin weighs 40 pounds. Blocks 12 inches in diameter, necessary for the testing of larger calibers, weigh 100 pounds. To test something like a .45-70 Government requires two of these monster blocks. The mixture ratio of 10% gelatin is 1 part Knox gelatin and 9 parts water. We mix the gelatin with hot water, pour it into molds and refrigerate for at least 72 hours.
When it is time for the test, we remove the chilled gelatin blocks from the refrigerator and move them to the shooting range in the ballistic lab. To ensure a valid test, the blocks need to be tested to ensure they are the correct density. The procedure for doing this is to fire a BB from an air rifle into a corner of the block. The BB must be fired at a specific velocity (575-605 fps) and penetrate to a specified depth (2.95-3.74 inches). If the block is not the correct density, your results will not be valid. This test is an important step. Always look first for the BB when viewing gelatin test results. If there is no BB, you know the BB calibration may not have been done.
With calibration complete, we then shoot the gelatin block. Upon the impact and penetration of the projectile, the gel block swells. This is easily viewed with high speed photography. The gelatin will develop fissures or tears from the impact tearing through it. The damaged area is often in roughly the shape of a football. The projectile will then typically stop within an 18-inch block, unless the bullet is designed for deeper penetration or is nonexpanding. The gel bock contracts to original exterior dimensions immediately after impact. We then measure all dimensional criteria of the damage to the interior of the block and record the results. The damage to the block is easier to photograph if we use dye to provide contrast. So we use a syringe and catheter to inject dye into the bullet path of the gel block to add needed contrast. Dying the temporary cavity is not a technically necessary procedure for a valid test, but it does greatly aid in the ability to see the wound and photograph the cavity that was created. We then photograph the results to record the performance.
Nomenclature and evaluation
Now the fun part starts. This is the part of the task that allows us to examine results, learn how the round of ammunition performed on this particular test and compare performance to other ammunition tests or performance standards. There are standard performance characteristics that need to be compared. At Black Hills Ammunition we have also added some other measurements that we, or our customers, have concluded should be documented. In a nutshell, we want to know the following:
- How soon does the wound cavity start?
- How wide is the cavity at its widest point?
- How deeply did the bullet penetrate until the widest part of the cavity was formed?
- How long is the cavity?
- How deeply did the bullet penetrate?
- What fragmentation occurred?
- What is the retained mass and diameter of the projectile?
In addition to these standard questions, at Black Hills Ammunition we also record the point it appears that any bullet fragmentation occurred. Plus we measure how deeply the fragments continued to penetrate.
We measure the “Neck” of the cavity. The neck is the distance from the front of the block to the formation of the significantly damaged area, which we refer to as the “Temporary Cavity”. A short neck is generally considered desirable as this shows the wound cavity as starting immediately. A long “neck” could mean reduced effectiveness when shooting targets with a narrow cross section. The bullet could be wasting potential effectiveness by not creating the significant wound cavity in the right place.
Next we look at the dimensions of the temporary cavity. How long is it? (Temporary Cavity Length “TCL”) How wide is it? (Temporary Cavity Diameter “TCD”)? We look at where the cavity is located. This is important because you want the damage to occur in the vital area of your target. We measure to the location of the widest part of the temporary cavity, measured from the face of the gel block. We call this, not surprisingly, the Temporary Cavity Diameter Location “TCDL”. We measure the Maximum Penetration depth “MPD”, the weight and diameter of the recovered projectile, along with fragment piece count and their depths of penetration.
There is also a part of this that you will never see unless you are right there at the test, but we will share it with you. From the side it looks like one hollow wound cavity filled with red dye. Wrong. That mental picture results from a two dimensional photograph and two dimensional measurement, i.e., diameter and length. In reality the damage is not a hollow cavity of damaged area, but is actually a series of splits or fissures in the gel. There is no standard for quantifying the value of more or fewer fissures.
Comparing Gelatin performance to performance in live tissue
I said earlier that 10% ballistic gelatin is universally recognized as the most appropriate medium for simulating flesh, and measuring/predicting what a bullet should do on living tissue. So we should be able to simply superimpose gel test results onto a body, and see what the wound track would be, correct? No, not exactly. Gelatin is homogenous. It is the same density throughout. Living things are not homogenous. They have skin, bones, organs and tissues of different densities and degrees of elasticity. Bullets can react differently in bodies than they do in gelatin. Gelatin does give us a good idea of what to expect. It does allow us to get a good idea of relative performance of one ammunition to another, but it can’t easily simulate the differences that can occur with different body types or shot placements.
I can give a good example. For many years I shot deer with a .223 Rem. It was essentially what I could afford to shoot and what I shot the most. I got a good idea of what can be done with a .223 Rem on deer. I found that the 60-grain soft point worked well on deer, as long as I followed some rules learned the hard way. I learned to be picky on my shots. I shot deer within 200 yards, presenting a standing broadside shot. I shot them just behind the shoulder, through both lungs. When I shot a deer under those conditions, the deer went down just as fast as if they were hit with a larger caliber, such as a .308 Win. I would almost invariably find the bullet just under the hide on the far side of the deer.
When we started testing this 60-grain SP load in gelatin, I found what appeared to be an inconsistency. The FBI’s carefully determined criteria showed that the .223 Rem 60-grain SP load was likely to be ineffective due to insufficient penetration. The FBI standards were, of course, not developed to measure hunting ammunition effectiveness. They are concerned with human adversaries. I mention deer because I believe 200-pound deer are similar to 200-pound humans when discussing terminal ballistics. My deer hunting combination of a .223 Rem caliber rifle shooting 60-grain soft point bullets almost never penetrated to the 12-inch minimum recommended by the FBI. Yet the deer always died and I would find the bullet under the hide on the far side of the animal when skinning it out. So what happened?
The FBI recommendation for a minimum of 12-inches of penetration is based on ensuring the bullet is likely to penetrate deeply enough to reach the vitals. With a scoped rifle, a good rest, shooting discipline and lots of practice, I was able to place the bullet carefully avoiding major bones that could limit penetration. The bullet, after penetrating the chest cavity, would then go through the lungs which are not a very dense barrier, being essentially large air sacks. I would often hit the heart, but neither is that an extremely tough barrier. The bullet would then penetrate the far side chest wall, but by this time it had slowed and deformed into a smooth, expanded round frontal area. The bullet then encountered the hide on the far side of the animal. Animal hide is a very tough barrier for the now much slowed and expanded bullet. The hide acts similarly to a trampoline. It would almost invariably trap the bullet. The bullet did not just happen to stop there. The hide, being tough and elastic, actually caught the bullets.
One other factor in this situation is the opposite of what you might expect. The bullet slows in flight. By the time it covers 100 or 200 yards distance it has lost a good bit of velocity (starting at 3,100 fps it is 400 fps slower at the 100 yard mark) before impact. With the lower velocity, the bullet expands and fragments less and actually penetrates deeper. This was a case of a bullet actually penetrating further in flesh than the gelatin would predict.
The FBI recommends ammunition used for defensive purposes penetrate no more than 18 inches in order to limit the possibility of over-penetration. We are also aware of many instances where bullets that normally penetrate more than the FBI recommended 12-18 inches of gelatin regularly and predictably stop within bodies. The reason for this is similar to what I related from my deer hunting experience. The hide on the far side catches the bullet. I have heard estimates that skin on the far side is equal to an additional 4+ inches of gelatin. I would guess these estimates are probably pretty close. That would also explain many of the large caliber deer hunting bullets that end up as treasured hunting mementos, having been pulled from under the far side of a deer.
What does all this mean? I agree that 10% ballistic gelatin is currently our best method of testing ammunition for terminal performance. It is a standard that can be replicated in controlled circumstances by different ballistic labs. It closely replicates what happens when bullets strike flesh. It is not perfect, but it is at this time the best test medium we have. It allows us to predict a level of performance, and make informed choices. In the end however, the best ammunition and projectile in the world is ineffective without shot placement. A technically inadequate caliber and bullet can however, be effective if placed correctly. It is tempting to study ballistics and pick the best new combination and get a false sense of confidence about our capability. It is wise to study in order to make good equipment choices, but in the end, the skill and the will are more important than the tools. Pick the ammunition that appears to be best suited for your task, whether it is hunting, training or self-defense, then dedicate yourself to refining what is most important, your skill.
This is the first in a series of articles where we put various rifle and pistols loads to the test in 10% ordnance gelatin in the Black Hills Ammunition Ballistic Laboratory. Stay tuned!