In my last article (Roll Out The Barrel), I touched on the subject of Twist Rate and presented the formula for determining how it is derived. One thing that I mentioned is that by manipulating the formula, answers for an unknown variable that comprise the twist rate formula can also be found. One of those variables, velocity, is what I would like to explore for this not-so-succintly-written article.
The optimum muzzle velocity from bullet length, bore size and twist rate: V = (L * T ÷ D² ÷ 3.5)²
T = Twist rate in 1 turn per inches.
L = Bullet length in inches.
V = Muzzle Velocity
D = Diameter of the bore grooves in inches.
That seems pretty cut and dried don’t you think? It is actually not, because it is a false indicator, as is twist rate! As an example, and according to various sources, the optimum twist rate for the 9mm is 1:16. What is important to note is that the 1:16 twist rate is also used with the .40/10mm and the .45 (.451 diameter) cartridges. Also. the 1:16 twist rate (according to Brownell) is recommended for the 55-grain .223 round – as long as than velocity is more than or equal to 4,300 fps!
What I can surmise is that the 1:16 twist rate will stabilize bullets that weigh any where from 55-grain to 250-grain regardless of bullet design! It is what happens to the projectile once it leaves the barrel that is questionable, but to get there we first have to get the bullet out of the barrel. Velocity becomes the name of the game and velocity needs energy.
If I am simply using a bullet to punch holes in a paper target, then the bullet does not need a lot of energy. However, if I am hunting a large-game animal that bullet needs a lot of energy. If I am in a defensive situation where I have to use my PDA, the bullet(s) that I fire needs a lot of energy (among other things) to do the job that they are intended (by the manufacturer and me) to do – bring home game or to stop a threat that could be four-legged or two-legged.
To begin with, I am not a physic’s major, have not played one, nor have I studied physics in length. If anybody would ask me what “energy” is, I would have to respond with, “Red Bull in my morning coffee?” I am simply a person who is trying to gain a general understanding about what is happening within and without the firearm that I may be shooting at any given time.
There are many times when I am in a range session, regardless of the firearm being operated, and one or more bullets simply did not impact on the target at (or at least in the general vicinity) where expected. When bullets do impact the target where I expect them to, it is a jubilant time. But, there are many factors at play when we operate a firearm and “aim small, miss small” becomes the order of the day.
At a shooting session in the distant past, one of my shooting buddies aimed his Glock G19 for the first shot of his session. I was in the adjacent lane and observed the hole that the bullet left in the dead center of the bulls-eye. At that point I heard, “well, I can go home now!” He even took a picture of the target and I presented his expended casing to him to cherish and treasure forever. His beatitude was very brief, however. As he finished his session, his shooting result was among those of mortal men. However, for that one brief shot, he was among the gods. I was lucky to keep my shots in a 4-inch circle at the same distance, as I was shooting a pistol that I had not shot in a long time and was trying to adapt to the pistol and conquer my shots. Mentally and physically I struggled with myself and the pistol (and ammunition) until I was resigned to the fact that my shooting performance was less than stellar.
I had been shooting some Aguilla 124-grain FMJ through a Springfield XDs 4.0 9mm, switched to a factory-reloaded 124-grain FMJ, and then tried some reloaded 115-grain cartridges (re-loaded ammunition) provided by my Son-In-Law. All cartridges fired and bullets went out the barrel in the right direction, although there was a disparity in velocity with the three different sources of the cartridges. Of the three, the hand-loaded 115-grain cartridges performed the best, closer to my point of aim, but I have no idea why.
The Aguilla 124-grain FMJ is rated at 1115 fps at the muzzle and the factory reloaded ammunition was rated at 1150 fps. Looking up the loading recipe for the hand-loaded 115-grain cartridge (since my SIL did not provide velocity information), it was determined that the projectile would fly out of the muzzle around 1175 fps. I can attest that all three “brands” of ammunition did, indeed, penetrate paper and that was all that I asked of them.
The Aguilla ammunition; however, and on several occasions, failed to lock the slide of the XDs back on the last round. While some cartridges had enough energy to get the bullet out of the barrel, and did have enough energy to chamber fresh rounds, they did not have enough energy to properly lock the slide back. While bullets fired at low-velocity is not a concern with a revolver, it is a concern when the cartridge is used in a semi-automatic pistol or semiautomatic PCC. But, when the same ammunition was fired through the Ruger 9mm SR1911, there was no slide lock-back issues. I could only surmise that the recoil spring spring system in the XDs is of a heavier spring rate that that of the SR1911 recoil spring. But, I digress.
The question of velocity of a bullet vs. the twist rate of the barrel it is traveling through still weighs on my mind. Granted that a rifled barrel takes a lot of abuse from a bullet being forced through it, but at what point does rifling no longer matter? Is it the velocity of bullet travel or wear related? That question beckons like an article to be researched and presented at a later time to me. So, let’s get back to the matter at hand.
While I was preparing this article I thought about the many articles that I have read regarding the “best bullet for your barrel” of which could fill volumes. Most of the articles address the latest and greatest defensive rounds in the standard and +P configurations. Some articles even show performance data, chronographed by the author or others, in an attempt to exemplify or discredit a particular cartridge or series of cartridges. Normally, and to me, these chronographed results are deemed as useful information rather than a guiding light for future ammunition purchases. The cartridges are usually fired out of a firearm that I do not own, nor may desire to own, and the information presented is as desirable to me as a test pattern on a modern television (am I am telling my age?). What I care about is what is happening with the ammunition in MY firearm at the time it is being shot. Chronographing only tells me the velocity of a bullet out of a given barrel at a given time under a set of given influences; it is not impractical data, but it is not empirical data either.
What we do know about velocity, as related to firearms, is that velocity is speed with direction with the barrel of a firearm providing the direction. The rifled barrel of a firearm; however, is a constrictor and does not provide velocity to a bullet but does; however, have a lesser or greater affect on a bullet’s velocity. The less constriction on a bullet in a barrel, the less the influence on a bullet’s velocity the barrel exhibits.
In referring to the Fifth Edition of Ammo & Ballistics, which I use as a general guide in selecting cartridges, I can find 9mm 124-grain bullet-weight cartridges that vary in velocity from 1096 fps to 1250 fps for bullets types ranging from FMJ to HP in various manufactured configurations.
Bullet velocity is measured under certain conditions; two if which is barrel length and twist rate. According to the Fifth Edition of Ammo & Ballistics, all 9mm ammunition is tested using a 4-inch long barrel with a 1:10 twist rate. Notice that the number of lands and grooves is not mentioned.
For each commercially-manufactured cartridge listed (rifle or handgun), bullet data is presented at the muzzle and out then to 200 yards (in 25 yard increments) for handgun cartridges and out to 1000 yards (in 100 yard increments) for rifle cartridges. SAMMI specifications (bullet weight, velocity in fps, and maximum average pressure) are provided for each bullet weight; in 9mm, bullet weight varies from 88-grain to 147-grain in the most common bullet configurations.
Taking a selected cartridge, the Speer 124-grain GDHP (23618), a common and promoted self-defense cartridge, the following measurements are provided (at the muzzle):
- Velocity in feet per second = 1150
- Energy in foot-pounds = 364
- *Taylor KO Index = 7.3
- Mid-Range Trajectory Height in inches = 0
- Drop in inches = 0
Note that these figures are straight out of the barrel with no consideration for sight height, which would be indicated by “Drop in inches.” For example, if the sights were 1.5″ above the bore-line, the Drop in inches at the muzzle would equal -1.5.
* Taylor KO Index
The Taylor KO Index has been determined by Chuck Hawks (and others), to be “… antiquated, inaccurate and should not be used as a reference in stopping power discussions.” As Mr. Hawk also noted, that many gun writers often use the Taylor formula when talking about “stopping power.” As you can see, the 5th Edition Ammo & Ballistic book uses the Taylor KO index, but to the book author’s credit, reference is made to other sections in the book that discuss the Taylor KO Index in greater detail. Given the studies conducted by Hatcher, Thompson, LaGarde, Sanow, Marshall, and Fackler, it is up to the reader to decide if the Taylor KO Index is even worth bantering about. However, I have included the Taylor KO Index here simply because it is included in the book.
Now, let’s look at a second example, the Speer 115-grain GDHP (23614)
- Velocity in feet per second = 1210
- Energy in foot-pounds = 374
- Taylor KO Index = 7.1
- Mid-Range Trajectory Height in inches = 0
- Drop in inches = 0
For giggles, let’s compare the ballistic data for each of the two cartridges at 50 yards:
Table 1. Ballistic Data – Speer GDHP at 50 Yards
|Ballistic Category||Speer 124-grain GDHP (23618)||Speer 115-grain GDHP (23614)|
|Velocity in feet per second||1039||1071|
|Energy in foot-pounds||297||293|
|Taylor KO Index||6.6||6.2|
|Mid-Range Trajectory Height in inches||0.9||0.8|
|Drop in inches||-3.5||-3.2|
The above is all relative data, as no chronograph is absolutely precise and any number of variables can affect a chronograph’s performance when measuring the velocity of bullets. Also, the test barrel that produced these results is not the same barrel through which I am shooting these cartridges. In other words, take the results with a grain (no pun intended) of salt. And, I will tell you why.
As I mentioned, the source for this information is the Fifth Edition of Ammo & Ballistics. However, if I visit the gundata.org website, and select the Speer 124-grain GDHP cartridge from their projectile parameters list of cartridges, the muzzle velocity is listed as 1220 fps. while that is only 10 fps off the velocity shown in the book, 10 fps can make a difference in downrange performance – to include bullet trajectory.
The above shows why I take any measurement with a grain of salt; there are no absolutes!
SPEED = DISTANCE/TIME
This is an important distinction. Velocity is a vector, it includes direction. Speed is a scalar because it doesn’t specify which direction something has moved, simply that it is displaced a certain amount at a certain rate. The formula works for velocity because often people will use the term velocity when they mean speed, but really it is the formula for speed (if you see a formula looking for velocity, just know that they are actually looking for speed).
With a ballistic chronograph, velocity is determined by dividing distance between two detection “screens” by the time it takes the bullet to pass through both screens. Modern chronographs use optical sensors to detect the bullet’s passage, but the term “screen” has stuck as a carry-over from the early days of chronographs. High frequency counters (“clocks”) measure the time that a projectile passes “from Point A to Point B” precisely. Modern ballistic chronographs, with their extremely fast clocks, theoretically allow the use of shorter inter-screen distances since time is measured more precisely due to there being more “counts” per second.
It is important to note that ammunition manufacturers typically measure rifle bullet velocities using a 24-inch test barrel. As a rule of thumb, for every additional inch of barrel length beyond 24 inches, the velocity increases by 20 feet per second. Likewise, for every inch of barrel length below 24 inches, the velocity decreases by 20 feet per second. For example, if your rifle barrel is 20 inches long, then subtract 80 feet per second from the manufacturer’s stated velocity. There is no such rule of thumb for pistol ammunition.
With factory loads, of course, we are at the mercy of the manufacturer and manufacturers tend to lean on the best side of liability, as do manufactures of cartridge components like cases, primers, powder, and bullets. Most, if not all, manufacturers of bullets who also cater to the hand-loading community advise against loading to the maximum pressures (Copper crusher or Transducer) to be on the safe side; recommended cartridge recipes for hand-loader are usually 10% to 20% lower than the maximum loading. However, for years hand loaders of ammunition have tested the waters, pushed the limits, and have given us many fine high-powered cartridges. Through the efforts of Elmer Keith, the first magnum revolver cartridge, the .357 Magnum, as well as the later .44 Magnum and .41 Magnum cartridges, ushered in many producers of “wildcat” cartridges that since have become standard cartridges for many.When I was competing in police bulls-eye matches, I rolled my own competition ammunition. The bullet used for competition had to be of the wadcutter design, but no other requirements were designated. The .38 special wadcutter bullet, when run through the barrel of a Smith and Wesson Model 686 4-inch revolver at “target” velocities is very pleasurable to shoot. Wadcutter bullets leave a nice round hole in a paper target and target strikes can be easily determined and counted. Cases were loaded with 148-grain wadcutter bullets, just enough powder (Alliant Bullseye) to obtain a 25-yard zero, and regular Small Pistol primers, which produced a low-recoiling projectile with the least amount of muzzle drop at 25 yards as I could manage. That was really all that I required out of these “Target” rounds. Through some experimentation, I found that I could load the same bullet in a .357 magnum case with the same powder and charge and gain a little more accuracy. However, I had to add some “fiber-fill” to the case to fill the additional space caused by the longer magnum case.
At one point during competition, and due to the fact that a competitor noticed that I was using a longer length case, I had to submit several “sample” cartridges for chronographing to prove that, although I used longer cases, the ballistics were well within .38 special ballistic limits. Since there was no restriction as to case length, I was allowed to continue using the .357 magnum cases. The reason for my using the .357 casing was for accuracy purposes. I figured that if I could shorten the “leade” time, the time for the bullet to engage the barrel’s rifling, it just might result in a touch more accuracy. While I did experiment with some powders that would better fill the case and decrease the amount if fiber-fill, the experimenting was short-lived and brought to a halt after I left competing.
POWDER BURNS AND THE CHARTING THEREOF!
For those who hand-load their own ammunition, powder burn rate causes a good amount of banter. However, two conventions seem to be constant; long barrels require slower burning powders; whereas, short barrels need fast-burning powders.
The ideal combination for the hand-loader that you want to achieve maximum loading density with a propellant that launches the bullet to the highest velocity without exceeding the industry-specified MAP and also delivers the desired accuracy. Loads that almost fill or even slightly overfill the case (i.e., typically not more than 5 percent compression) and achieve near maximum MAP are considered to be the most efficient.
Light charge weights of fast-burn-rate propellants are loaded in small, lower-pressure, straight-walled cartridges. Heavy charges of slow powder go in large, bottle-necked, higher-pressure rounds. As the cartridge capacity increases and/or the SAAMI pressure limits increase, the best propellant will typically exhibit a relatively slower burn rate. Since I only loaded for a few handgun cartridges, the light charge weights of fast-burn-rate propellants were suitable for my purposes. I pretty much went by the re-loading manuals that I had at hand to guide me in powder, primer, and bullet selection for standard and magnum cartridges. I knew that fast and slow powder burn rate made a difference, but I did not educate myself at the time by reading Burn Rate Charts from various powder manufacturers; I just took my cues from reloading manuals without knowing why a certain powder was listed that would provide me with my desired results.
Burn Rate Charts can be an excellent resource in determining what powders may work for your application(s). By viewing this short list, you can see why those who hand-load may have an over-abundance of powders. My rule of thumb, during my had-loading days was “Buy a pound, work it down” and that kept me in check when wanting more powder to experimentally burn. Since most of my shooting was with handguns (.38/.357 magnum, .45 acp, and .44 magnum) I tried to keep my powder ownership to just a few powders.
Here is just a sample of propellants that are listed from Fastest to Slowest:
- Norma R1
- Winchester WAALite
- VihtaVuori N310
- Alliant e3
- Hodgdon Titewad
- Alliant Red Dot
- Hodgdon Clays
- IMR Hi-Skor 700-X
- Alliant Bullseye
- Hodgdon Titegroup
- Alliant American Select
- Accurate Arms Solo 1000
- Alliant Green Dot
- IMR Trial Boss
- Winchester Super Handicap
- Hodgdon International
- IMR PB
- VihtaVuori N320
- Winchester WST
- Accurate Arms No. 2
- IMR SR7625
- Hodgdon HP-38
- Winchester 231
- Alliant 20/28
- Alliant Unique
- Hodgdon Universal
- Alliant Power Pistol
- VihtaVuori N330
- Alliant Herco
- Winchester WSF
- VihtaVuori N340
- IMR Hi-Skor 800-X
- IMR SR4756
- Accurate Arms No. 5
- Hodgdon HS-6
- VihtaVuori 3N37
- VihtaVuori N350
- Hodgdon HS-7
- VihtaVuori 3N38
- Alliant Blue Dot
- Accurate Arms No. 7
- Hodgdon Longshot
- Alliant 410
- Alliant 2400
- Accurate Arms No. 9
- Norma R123
- VihtaVuori N110
- Hodgdon Lil’Gun
- Hodgdon H110
- Winchester 296
- IMR IMR-4227
- Hodgdon H4227
- IMR SR4759
- Accurate Arms 1680
- Norma 200
- Alliant Reloder 7
- IMR IMR-4198
- Hodgdon H4198
- VihtaVuori N120
- Hodgdon H322
- Accurate Arms 2015BR
- VihtaVuori N130
- IMR IMR-3031
- VihtaVuori N133
- Hodgdon Benchmark
- Hodgdon H335
- Accurate Arms 2230
- Accurate Arms 2460
- Hodgdon H4895
- VihtaVuori N530
- IMR IMR-4895
- VihtaVuori N135
- Alliant Reloder 12
- IMR IMR-4320
- Accurate Arms 2495BR
- IMR IMR-4064
- Norma 202
- Accurate Arms 2520
- Alliant Reloder 15
- VihtaVuori N140
- Hodgdon Varget
- Winchester 748
- Hodgdon BL-C(2)
- Hodgdon H380
- IMR IMR-4007SSC
- VihtaVuori N540
- Winchester 760
- Hodgdon H414
- VihtaVuori N150
- Accurate Arms 2700
- IMR IMR-4350
- Hodgdon H4350
- Accurate Arms 4350
- Norma 204
- Hodgdon Hybrid 100V
- VihtaVuori N550
- Alliant Reloder 19
- IMR IMR-4831
- Accurate Arms 3100
- VihtaVuori N160
- Hodgdon H4831 & H4831SC
- Winchester Supreme 780
- Norma MRP
- Alliant Reloder 22
- VihtaVuori N560
- VihtaVuori N165
- IMR IMR-7828
- VihtaVuori N170
- Hodgdon H1000
- Hodgdon Retumbo
- VihtaVuori N570
- Accurate Arms 8700
- Hodgdon H870
- VihtaVuori 24N41
- Hodgdon H50BMG
- Hodgdon US869
- VihtaVuori 20N29
Out of the propellants listed above, I only used a handful of them: Hogdon H110, Alliant Unique, Winchester 296, and Alliant Bullseye were my primary powder choices.
I no longer hand-load, so like many of us, I am at the mercy of ammunition manufacturers and rely on their cartridge expertise to get the jacketed lead out of the barrel and into a target. Once in the target, it is up to the bullet’s design to perform as the manufacturers’ claim it will.
Now, I would like to jump backwards a bit to my 9mm shootout. I listed Speer GDHP ballistic difference for 115-grain and 124-grain bullets. But, what if I add the Speer 147-Grain GDHP to the mix for the same distance of 50 yards?
Table 2. Ballistic Data – Speer GDHP at 50 Yards
|Ballistic Category||Speer 124-grain GDHP (23618)||Speer 115-grain GDHP (23614)||Speer 147-grain GDHP (23619)|
|Velocity in feet per second||1039||1071||932|
|Energy in foot-pounds||297||293||283|
|Taylor KO Index||6.6||6.2||7.0|
|Mid-Range Trajectory Height in inches||0.9||0.8||1.2|
|Drop in inches||-3.5||-3.2||-4.6|
One noticeable factor is the Taylor KO Index. Compared to the 115-grain and 124-grain versions of the GDHP, the 147-grain GDHP is heavier, and the energy is less, but the Taylor KO Index number is higher – interesting for sure.
THE BALANCE OF POWER
According to a Wikipedia article – Muzzle Velocity: “In conventional guns, muzzle velocity is determined by the quality (burn speed, expansion) and quantity of the propellant, the mass of the projectile, and the length of the barrel. A slower-burning propellant needs a longer barrel to burn completely, but can, on the other hand, use a heavier projectile. A faster-burning propellant may accelerate a lighter projectile to higher speeds if the same amount of propellant is used. In a gun, the pressure resulting from the combustion process is a limiting factor on projectile velocity. A balance between propellant quality and quantity, projectile mass, and barrel length must be found if both safety and optimal performance is to be achieved.”
While I can just about guarantee that the bullets installed in the cartridge cases listed in the tables will exit the end of the muzzle in a pistol, revolver, PCC or PCR, there is much more to the story.
Whether hunting or in self-defense, opinions about the performance of the tools that we use (firearm and cartridges) cannot be viewed from a standpoint of simple reviews or cartridge statistical data. Just because we are running the “best” ammunition through the “best” firearm does not guarantee “best” results. In other words, it’s what you observe that matters.
So, the trigger is pulled, the primer is struck and ignites the powder, the powder is burning off at some rate, the projectile is forced out of the barrel and is heading downrange under the influence of lands and grooves. Note that the muzzle velocity may not be the same as when the cartridge fires and the projectile first leaves the cartridge case. Downrange velocity of the projectile can be accurately measured through chronographing or simply calculated using a series of variables and very extensive formulas.
Now, we get into the area of “Terminal Ballistics” that is determined by yet another set of variables.
In an article by Cleve Cheney…
“Looking first at the bullet and its terminal performance, here are some of the variables that come to mind (there are likely to be many more which I may not have taken into consideration):
- The dimensions of the bullet (length and diameter) and changes that might occur as it is passing through living tissue, e.g. increasing diameter in expanding bullets.
- Its impact mass and mass through the target (which will progressively decrease, and be largely determined by its ability to stay together, and influenced by the types of tissue encountered along the wound channel).
- Its impact velocity and velocity through the target (which will progressively decrease and be influenced by the types of tissue encountered along the wound channel).
- Its rotational energy and momentum at the point of impact and through living tissue.
- Its impact momentum and momentum through the target (which will progressively decrease and be influenced by the types of tissue encountered along the wound channel).
- Its impact kinetic energy and kinetic energy through the target (which will progressively decrease and be influenced by the types of tissue encountered along the wound channel).
- The shape of the nose (angle of the ogive, ball, spitzer, flat nose etc.) and how it may change as it passes through living tissue).
- The incident angle (i.e. the angle of the bullet as it impacts the target) – yawing, tumbling, flying straight, etc.
- Rate of energy transfer.
- Effect of the bullet caused by the density of tissue at the initial point of contact and along the wound channel.
- The cohesive properties of the bullet (i.e. its ability to stay together and not break up) which will be determined by its construction
- Soft nose, ballistic (plastic) tip, monolithic or FMJ construction.“
Then, add to the balance of power equation, the effect of any given projectile on a target of flesh, bone, and muscle. That is a topic for another day.
Inevitably, +P ammunition will come up in the conversation when talking about velocity. Some folks treat +P ammunition as a godsend to their favorite caliber. Let’s take a look at a couple of relationships between standard and +P ammunition for the 9mm:
- 9x19mm: 124 grain bullet at 1140 fps
- 9x19mm +P: 124 grain bullet at 1200 fps
Obviously, there is a gain in velocity with the +P loading. But, what do we really gain?
Let’s look at a “Relative Stopping Power” comparison between a standard and +P 9mm load:
- 9x19mm = 80% (Winchester 115 grain Silvertip JHP)
- 9x19mm +P = 89% (Winchester 115 grain JHP)
We get a modest increase in “Relative Stopping Power” with the +P load, but again, what do we gain? Well, we might gain a new recoil spring of a higher spring rate than we use for standard loads just to handle the ferocious beating the pistol is placed while shooting +P loads. Plus, you gain more felt recoil and muzzle flip. In my mind, if I needed more power, I would simply step to the next caliber; the .40 Smith and Wesson. But, as we are finding out, law enforcement agencies are returning back to the 9mm from the .40 Smith and Wesson for several reasons; advances in 9mm ammunition ballistics has made the cartridge better in terms of performance without the snap of the recoil with the .40 Smith and Wesson cartridge, and officers with recoil sensitivity are more comfortable shooting the 9mm cartridge. With that said, one of my favorite pistols to shoot is the 1911 platform chambered in 9mm (the original chambering for the 1911); a simple recoil spring change and the pistol is set up for higher velocity cartridges, such as Cor-Bon 125-grain JHP +P (SD09125/20) at 1250 fps at the muzzle, which places this 9mm cartridge above most .40 Smith and Wesson cartridges.
RUNNING TO EMPTY
I’ve taken you this far in a somewhat fgeeble attempt to explain that a lot of what we read and hear are just reference points that may help you to form a good understanding of what pushes a projectile past the muzzle of your firearm. Beyond that point, the rest is all speculation based on recorded data and/or mathematical supposition and should not be relied upon as fact.
If you have read the article “Roll Out The Barrel” you will have learned about some of the things that assist a projectile in stabilized flight. But, in order to place a projectile into stabilized flight, the projectile must first be subjected to a lot of force in order to leave the barrel and I hope that I have provided some fuel for you to do your own research on barrel-to-bullet compatibility.
- Velocity Time and Distance Ultra Calculator: http://www.1728.org/velocity.htm
- Living With A Chronograph: http://www.frfrogspad.com/chrono.htm
- Why Powder Burn Rate Is Meaningless: http://chuckhawks.com/powder_burn_rate.htm
- Muzzle Velocity: https://en.wikipedia.org/wiki/Muzzle_velocity
- Debunking Ballistic Myths: http://www.africanxmag.com/debunking_ballastic_myths.htm
- +P Handgun Ammunition (.38 Special, 9x19mm, .38 Super and .45 ACP): http://www.chuckhawks.com/handgun_P_ammo.htm
- Taylor KO Factor: https://en.wikipedia.org/wiki/Taylor_KO_Factor
- Terminal ballistics: https://en.wikipedia.org/wiki/Terminal_ballistics
- Ballistic pendulum chronograph for determining bullet velocity, explanation and demonstration: https://www.youtube.com/watch?v=WYgDoynkZ1M