In 1988, the FBI produced the first protocol for testing ammunition after the 1986 Miami shootout. The test was developed as a laboratory method to test bullets for performance before use by law enforcement.
Gel
The test is specified as a 10% gel mix which is 1 part 250 Bloom (developed in the 1920’s) dissolved into 9 parts warm water and cooled. The block is often referred to being calibrated by a .177 bb at 600 ± 10 ft/s, and to result in penetration between 3.3 and 3.7. FBI standards show that all shots shall result in 12-18 inches of penetration.
This is just the summary of the test but I wanted to dig deeper. In 2016, I read “Bullet Penetration” written by Dr. Duncan McPherson. He references ballistics gelatin as the baseline standard and even developed a method for compensation in the case that the calibration is off by up to 2 inches in either direction. Handy, but this opens the door to a much larger picture.
Technology Advances
While this test is considered old in my book, the development of ammunition has changed drastically in the past 3 decades. With open access to the internet, improvements in high speed cameras, and not much update on the testing, we all fall victim to misinformation and keyboard warriors. Generally speaking, the stereotypical gun owner does not necessarily trust the FBI, except for how to test ammo…interesting.
The main issue with gel is the lack of variability, misunderstanding of wound cavities and the over-reliance on kinetic energy figures.
Failures of Ballistics Gel
Ballistic gel is a as a homogeneous material. This creates a false reading to show how a bullet will react to different materials. Think watermelon vs steel. Lots of fun internet channels show fun test blowing up watermelons (What a waste!) and a bullet passes through easily. One of the most famous pioneers in the world of handgun hunting, Mr. John Leinbaugh, highlighted this in one of his famous seminars. While testing numerous big bore hunting loads in gel and wet newsprint, he showed off a .44 magnum load that would penetrate about 36 inches in ballistics gel. While this looks stout, he proved it to be misleading by placing a bone from a cow shoulder in front and repeating the shot. The test showed a result of bone penetration and then only about 4 inches in to the gel.
My Thoughts
This was the beginning of a phrase I would use to generalize bullet performance.
“All bullets in different calibers react differently against different materials at different velocities”. If you have 3 calibers, 10 bullets, and 3 bullet weights for each, that’s 90 combinations. I just made that up, there is a lot more out there. Not to mention the exponential increase when you look at the various materials when a human body and the variation in muzzle velocity of different barrel lengths.
Initial Impact
Another notice in conversation is the understanding of temporary cavity. This was something often discussed by handgun hunters but not something that is drastic enough to warrant discussion. Temporary cavity is usually what’s referenced when discussing the “bubble” or void that occurs when a projectile shocks the impacted material out away from the impact location. This phrase somewhat went away until high speed cameras became more common in recent years on our favorite Youtube channels. When gel is hit with a large and fast bullet, a dramatic bubble occurs, and I’ll admit, looks really cool. However, many are starting to understand that this can be misleading. It’s not that simple. While a shockwave can go through soft tissue on impact, even with high-speed cameras focused on deer, I have yet to see one expand so greatly.
Gas
From our test and some theory, many are learning why this happens in gel, specifically. During test, we often see a puff of gas that escaped out of the entrance point. That gas that comes out has to come from somewhere and is shown to be material that has turned into a gas from the heat caused by friction from the bullet. Given that the ballistics gel is approximately 90% water, we can assume that the gas is 1600 times less dense than water, the volume of a small amount of the gel can take up a lot of space when turned into vapor. Too add to this, the structure surrounding the gas bubble does make a significant difference due to simply having more material to fight against the pressure developed in the bubble and also the relative perception of the size of the bubble against the block of gel. To put it simply, a gel block that is 12” x 12” on the cross section will not appear to have as large of a bubble as a 6” x 6” would.
Water Jugs
An easier way to understand this, is the water jug test. Hydrostatic force is often used to describe the formation of the temporary cavity. Given that water is not compressible, when force is applied to the water, the resulting pressure is evenly distributed throughout the entire area. Often times a water jug is shot and that resulting pressure creates a great explosion! I’ll also admit, it’s good old-fashioned fun for me. However, it’s not realistic in any way. If you fill the water container all the way, it’s more likely to happen, but if you reduce the water by about 20%, very little reaction occurs. There are other variables such as structure of the container and how it’s sealed but that’s for another time. If you just test to see how many water jugs your bullet penetrates, congratulations, you can now determine a great load for water jug season.
The Equation
With high-speed projectiles also coming into play, the discussion and obsession with kinetic energy comes up time after time. In case you live under a rock or fell asleep in physics class, the standard equation is KE= ½ MV^2 and results in a unit of foot pounds. As we all know, when working with a specific caliber, changing bullet weight is inversely proportional to bullet velocity. There are exceptions but that’s the general rule.
In general, that kinetic energy does get “absorbed” but transferring energy doesn’t take down an animal or an intruder. Every animal is absorbing energy as it eats, who cares? The energy has to be used to break something. Weather it’s a lucky shot on the central nervous system, break bones to incapacitate the structure, make it into the critical organs and disrupt blood flow, but also, with a typical mushrooming bullet, don’t forget that the bullet uses a lot of that energy in order to deform.
Kinetic
The issue here is that when someone tells me the kinetic energy of a bullet in ft-lbs, and I ask what that means, I’m usually met with a blank stare. Bigger is better so let’s get the lightest bullet we can find and run it as fast as possible, right? The best way I can get someone to relate is like the horsepower of a motor, you can have a 1000 HP motor that has high torque but a low top speed, a high speed motor with low torque, or something in the middle. You can also present this as a 175 grain .308 at 2400 ft/s it like my truck hitting me at 4 ft/s. Same kinetic energy, I guarantee one is going to hurt less.
The Math
At this point I can take it to a more dynamic view.
I know the word “calculus” may bring up some bad memories but hang with me here. In calculus, the derivative of an equation is the approach to show the sensitivity to change. If you take the derivative of kinetic energy with respect to the velocity (hopefully mass doesn’t change), you have momentum which is mass times velocity (p=mv). In this case, the mass is constant and the velocity being the continuously changing variable. Now, the momentum equation makes people think a bit differently, you can change the variables the same way but this is an easier way to see the balance. However, this also make it easier relate to the action of a bullet against material.
The kinetic energy formula is 100% valid, but more isn’t better. The “energy” has to be controlled. Generally, it goes to 4 main things:
1) Breakage/momentum of target material
2) Friction/heat
3) Sound
4) Bullet deformation
Much more energy is loss to bullet deformation than people realize. Yes, an expanding bullet is great for creating a larger cross section to cause more damage and a higher chance of hitting an artery, nerve or other incapacitating part, but if the bullet can’t get to those locations, it is useless. That is why proper controlled expansion is needed from manufacturers.
Force
Every material takes a certain amount of force to break, the bullet must exert that force and thus the “energy transfer” (another misused term) occurs. Don’t forget, the material is applying an equal and opposite force on the bullet. Now, the bullet isn’t magic, that energy is used to break whatever material, the bullet does 2 things; it slows and deforms. If you take the force equation (Force=Mass * Acceleration), the force on the bullet is set per the material (bone, muscle, organs), so a lower mass bullet will result in a higher rate of deceleration which can also cause easier deflection.
A heavier bullet will decelerate at a lower rate. Keep in mind, for discussion this is assuming a constant caliber, bullet profile and bullet construction. From a bullet manufacturing standpoint, the construction is what is changing, and while normal bullet construction wants to maintain all the mass, some are learning that you can still get impressive penetration depth after weight loss by creating a very efficient profile and delaying until organs are in contact. Keep in mind that controlled deformation is valuable, not just mushed up lead.
Some bullets to shed into shattered pieces everywhere. I have heard some people say “Oh, the surgeon is going to hate me!”. What did the surgeon do to you?. While I believe many companies fail and make gimmicky bullets that look cool in gel, in general practice, I don’t rely on them. Some have learned to have large, pre cut petals that have delayed release that will break bone, maintain mass, continue with reasonable velocity and then use intelligent hydraulic design to break at pre-stressed locations, and the base material that remains develops an incredibly efficient profile (think aerodynamic but through solids). Tiny little pieces, if they manage to penetrate organs, do minimal damage do to the elasticity of the organs. They will require surgery later, but will not result in detrimental loss.
Greatest Mind
As I mentioned before, one of the greatest minds when it comes to this topic is Dr. Duncan MacPherson. His book for my initial research became my bible. While there is no way to quickly summarize his work, the main equation that is used is known as Poncelets Ballistic Modeling. What this equation does it take certain target material specifications and bullet profile shapes to determine the total depth that a bullet will go into that specified material. This also assumes the use of solid bullets that do not deform. Calculating the work loss from bullet deformation is difficult to calculate and predict. Thanks to some creative minds on our team, this equation was reworked to develop a computer model that would show the velocity change of a bullet going through a certain thickness of a certain material. From live fire testing, this proved to be accurate within a few percent.
Knowledge
With the new dynamics of ammunition development and the growing use of social media and marketing agencies, I feel that the average person needs to understand what they are using for hunting and especially for defensive uses and a responsible gun owner, and not just buy the box of ammo with the coolest name and design.
To simplify the testing of ammunition, while adding more variables, we developed a similar “box” that has the layers of material that mathematically mimic the mechanical properties and thickness in which a projectile may interact with in a defensive shooting. Thicknesses have to be assumed simply because every location hit on a torso will have different results and everyone is different. It would be responsible to favor someone who is “more robust”.
Intruder in a Box
This is the thought process to the years of research behind the development of the “Intruder in a Box”. To add to the issues with ballistics gel, often multiple shots are taken on a small 6” x 6” section of ballistics gel, and the following shots interact with torn material from the prior shot. This can give a false result due to the structure of the gel being broken down and resulting in less resistance. The Intruder in a Box, while it does use sheets, has individual liquid chambers to prevent this. Any pistol round or small rifle that is on the target, will not have any effect on succeeding test shots.
I began writing this as a way to change how folks think about their ammunition choices, but looking back on some development meetings with some major manufacturers, I realized one thing… They have their hands tied. I had 3 meetings with engineers at one of the most popular bullet manufacturers and there was huge interest in this new test. However, when the ammunition they spent insane amounts of money developing, that passed gel test, failed in this new test, I was immediately shunned. I realized that they rely on government contracts so much that they don’t want to develop with any new test methods. I get it, it’s business, but it sucks. Even folks at the government research level like this but there is the governments infinite bureaucratic loop of “we are told to do this and that’s that”. No idea who demands it and no one wants to stick their neck out to improve anything.
Conclusion
Overall, the standards of testing ammunition need to be updated. The test needs to be easier to use for the average user, more dynamic than the outdated ballistics gel, and easier for the user to understand and not fall for any marketing gimmick. The variables are vast in the world of terminal ballistics. Ammunition is advancing, let’s bring up our understanding of how it works.
One response to “Ballistic Misnomer by: Joey Leblanc”
Great read.