Energy, Velocity and Knock-Down Power

By Bob Campbell published on in Ammunition

Recently, I received a challenge about the relationship between velocity and firearms performance. Velocity means a lot, but so does acceleration. Mass cannot be separated from energy and neither can velocity, but sometimes, we give velocity too much credit when it comes to energy tables. We must understand what is happening; it is as simple as understanding horsepower and torque in a vehicle engine.

Ballistics 101

A young, dark haired boy shoots a black .223

This young shooter likes the .223 because of low recoil and high velocity, which impart killing power.

Torque gets things moving, while horsepower keeps them moving. There is a peak efficiency of torque. When it comes to firearms—particularly powerful rifles—there is also peak efficiency, and those that are not so efficient produce overbore conditions. Many times, folks quote energy and try to predict the effect of a projectile on energy alone. Of course, outside and external ballistics are not as interesting as terminal ballistics. In addition, if the target is a woodchuck or a moose, that is the bottom line—terminal ballistics.

When it comes to penetration in any type of material, energy is not a predictor. Velocity and bullet construction are the predictors. Quoting energy works well for comparing different loads, but it does not mean anything. Analysis of the effect of a bullet, size of the wound or damage to ballistic media is what really matters. The problem of measuring wound potential cannot be done with energy. After all, Newton’s law describes forces, not energy, and velocity is important because it drives the projectile.

If you want to propel a 150-grain, .308 caliber bullet into a deer at 100 yards, you need a certain amount of velocity, a certain retained amount of energy, for the bullet to stay effective. If you engage the target at a longer distance, you need more velocity. If hunting larger game, particularly at a greater distance, you must increase the velocity to ensure good bullet performance. You cannot get by with mediocre ballistics. That is the difference between the .30-30, .308, .30-06 and .300 Magnum. So, velocity is important because it drives the bullet.

The bullet exits the barrel at a given velocity—and a given energy, if you insist—then begins to shed speed. The advantage of high velocity (the greatest advantage, in my book) is that higher speed allows a trained rifleman to use less hold-over. A good example is the fast-stepping 3,000-fps .223 Remington. Naturally, a bullet weighing three times as much as the light 55-grain .223 will produce more recoil. There is no free ride, so we keep things reasonable. Just the same, a 150-grain bullet at 2,700 fps from a .30-06 is markedly easier to connect at longer range than the .30-30 WCF at 2,200 fps.

A brown handled rifle with a green strap lying on top of a dark gray jeep.

While velocity is part of the picture, it is not everything. But this all-around hunting rifle has plenty of velocity and penetration. Energy is just a paper number.

Therefore, velocity is important. The bullet creates a wound, which is not the same as punching a hole. A drill punches a hole, but we do not consider how much energy it uses. However, torque is another matter. If you punch a hole in the target, it damages the pressurized system; blood leaks out, and the system shuts down. A more complex wound creates more damage, and the shutdown is quicker.

The confusion about energy stems from the fact that different bullets perform differently. As an example, the 150-grain FMJ .308 will create, at best, a needle-like wound. The bonded-core bullet, designed for moose and bear, will not expand quickly in deer-sized game. The Nosler Partition will do a better job than either at an impact speed of about 2,500 fps at a 100-yard target.

Energy is all the same, but velocity seems most important in our calculations.

Is there really a difference in the effect of the same bullet at different velocity? It depends. At different ranges, the heavier the bullet design, the less difference is noticeable in the wound at different velocity. A bullet designed to fragment or expand quickly shows more differences. As many of you are aware, the short-barrel .223 is a formidable weapon. However, once impact velocity drops below 2,000 fps, wound potential is dramatically affected for the worse.

Another important consideration is long-range accuracy. As long-range shooters know (and we are talking about more than 300 yards to well more than 500 yards), the challenge is maintaining transonic velocity. Once a load falls into subsonic range, accuracy becomes problematic. Long-range shooters try to keep the load at more than 1.2 MACH—that is 1 2/10 the speed of sound. Below that speed, buffeting and wind problems multiply to kill accuracy. Therefore, velocity is very important.

Velocity is also important because the other important factor is a constant—gravity. Gravity pulls on the bullet a bit slower the faster the bullet, and the less time in travel to the target, the less time for gravity to pull on the bullet (wind deflection is much more difficult to compensate). A fast bullet is vulnerable to wind drift.

8 .223 gold cartridges with copper tips

The .223 offers high velocity and shoots flat. That high velocity ensures expansion.

Wind drift is not well understood, and it is not the wind blowing on the bullet—far from it. Wind drift occurs when the bullet aligns on the wind vector. I think that is most important to understanding the effects of velocity when you are developing a long-range load and a highly accurate hunting load. When loading for long range (and handloading is the way to achieve stellar results), the concern is with average velocity, standard deviation and extreme spread of velocity.

Consistency is the key.

Handguns and Velocity

Despite developments, such as the .454 Casull and .500 Smith and Wesson, handguns are about short-range power. Therefore power, not range, is the key. In standard packing handguns, the 10mm and .357 Magnum rely on high (for a handgun) velocity. However, wound potential with a big bullet is still the best choice for personal defense. Always has been. The first cavalry pistols were large, really short rifles, shorter than carbines.

When the knights gave way to ritters (riders) in Europe, they favored horse pistols, which allowed soldiers to extend their will past saber range, although not too far. When the U.S. Military adopted revolvers just before the Civil War, they learned a lot about handgun ballistics.

The Colt Walker was a huge revolver, both powerful and accurate. There was clamor for a Colt revolver larger than the original .36 caliber, and the .44 Walker was the answer. The Dragoon was a slightly smaller weapon. The Colt Navy .36 also was popular because it handles quickly and is accurate.

However, the fast-stepping .36 was better as a personal defense revolver than a warfighter. The soft-lead .36 ball traveled fast enough to expand at close range. Wild Bill Hickok used other weapons, while treasuring his pair of Navy Colts long after metallic-cartridge revolvers were available. The relatively high-velocity .36 ball is comparable to a modern .38 Special hollow point. The problem was, at long range (which was common during the Indian wars), the lead ball slowed and did not expand.

The Colt Navy was quite accurate and among the first military weapons that allowed a hit at ranges past where the projectile was effective. The .44 Colt Army, when properly loaded, is not appreciably less powerful than the .44 Dragoon. By all accounts, the .44 Army was among the most effective military revolvers ever fielded. The soft-lead ball produced a wound superior, many believed, to the later .45 Colt.

3 boxes of Hornaday ammunition, a light tan box with red lettering, with 2 red boxes of ammo with a white label and red lettering.

Hornady’s first-class ammunition maximizes the .243, with plenty of velocity.

The first generation of metallic cartridges was not very powerful. The .32 Rimfire used in the Smith and Wesson No. 2 breaks at about 700 fps. Later, the centerfire .38 Smith and Wesson demonstrated less than 700 fps in a revolver barrel. When Colt chambered the Single Action Army for the .45, centerfire cartridge technology took a giant stride. The new cartridge combined a heavy .454-inch bullet with high velocity. At more than 900 fps, that load could accomplish what it was designed to do—drop an Indian war pony at 100 yards.

The Colt SAA was, arguably, the Army’s last pureblood horse pistol. The 1911 .45 also proved capable as a horse pistol, yet the SAA was the ne plus ultra of revolvers at the time. The .44-40 Winchester had a different cartridge, one that still finds favor. The .44-40 uses a smaller, faster bullet than the .45 Colt.

The 200-grain, flat-point, .427-inch bullet might generate 1,000 fps from a long-barrel Colt (modern handloaders using a good, tight revolver might do even better, but that is a different tale). For the first time, revolver shooters appreciated high velocity. The .44-40 is generally more accurate than the .45 and hits hard. It is a game getter; the .45 is the man stopper. Not incidentally, the .44-40 kicks considerably less than the .45 Colt.

I believe the .32-20 cartridge whetted the appetite of American handgunners for a high-velocity cartridge, leading to the Magnums. In the 1900s, savvy handloaders could load the .32-20 to 1,400 fps or so. It proved a great small-game cartridge. Around the world, the 7.62 Mauser and Tokarev gained reputations out of proportion for the size of their 86-grain, .308-inch bullets. When a bullet strikes bone, in particular, the high-velocity, hard-jacketed bullet proved decisive.

Speer .22 Magnum load, with a full cartridge on the left and 2 views of the spent cartridge on the right

Speer’s .22 Magnum load shows what velocity can do even with a small bore.

Interestingly, after a failure with the 9mm Luger, a well-known terrorist changed to the CZ 52 and never looked back. Carlos killed two Surete agents with the CZ and preferred it to all others. However, the most reliable mechanisms for wound potential in a handgun remain caliber and weight. The .455 Webley launches a 265-grain bullet at a modest 650 fps. Yet, the cartridge gained an impressive reputation. We do not usually regard the .45 ACP as a high-velocity cartridge and, in comparison, its 230-grain bullet at 830 fps is fast.

In handguns, velocity is most important as the instigator of bullet expansion. Without expansion, the small bores do not exhibit adequate wound potential (with all respect to the exceptional Tokarev). High velocity ensures the expansion of a well-designed bullet.

The 9mm Luger offers acceptable wound ballistics because modern loads may exhibit more than 1,200 fps with a JHP bullet. The .357 Magnum and .357 SIG are even faster. The .45 ACP gets things done in a simpler, more dependable fashion, in my opinion, but just the same, performs well with a 200-grain bullet at more than 1,000 fps. For target shooting, all you need is a bullet that cuts the paper. However, velocity is an important factor in handgun accuracy. As many 9mm shooters will tell you, cast bullets perform better at more than 1,000 fps in the 9mm Luger. Lower-velocity loads seldom prove accurate, in my experience.

A young dark haired girl in a gray t-shirt and tan pants shoots a .223 riftle with a green trees and a white house in the background

Light, powerful and fast, the .223 rifle is always a good choice.

In the end, velocity is important to the overall performance of any cartridge. But velocity is more important in rifle cartridges.

Velocity affects the cartridge’s performance at every level and remains an important predictor of performance.

What is your favorite ammunition and why? Have you thought about the velocity vs. energy question before? Share in the comments section.



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Comments (5)

  • Pax


    Sorry guys. The most important factor is not the bullet – its the target. You pick your ammo based on the target not the characteristics of the ammo. In human and animal targets, you also have to consider hydroshock. The hydraulic shock wave of a hollowpoint 22 magnum rimfire can easily outperform a 308 FMJ if the target is mostly liquid or soft tissue but would be useless against the skull of a wild bore. Think target first, then figure energy, velocity and include hydroshock.


  • jeff


    I am glad I didn’t have this guy as a science teacher growing up. Energy and velocity are direct relationship, granted that a small increase in velocity yields a much larger increase in energy.
    The only thing that the author got right is that the bullet is really what is important. If you are hunting, then you need to use a bullet that will remain together, to minimize meat damage, if you are trying to stop somebody from killing you, then a bullet will do the most damage is what you want. IMHO, anyway.


  • larry


    I totally agree Flick. With a hand firearm a relatively slow, heavy projectile is by far more effective than a small fast projectile at self defense ranges.
    I’ll take my 45 acp over anything else in that situation every time.


  • Flick


    Im reminded of the workplace shooter with religious issues who shot up the hospital at Ft Hood using an FN 5.7.
    He wounded almost twice as many as he slaughtered, hitting several of them 4-6 times each.
    No knockdown power in that tiny hyper-fast bullet.
    If he would have been loosed in there with a .45,his tally would be much different.
    Same for that female Officer who fired on him and took him into custody.
    A proper firearm would have dispensed proper justice.
    There is a lot of thinking that should go into the selection of a firearm, not just a few basics.


    • Smitty 550


      It’s okay, Flick; It’s not too PC if you call him a Muslim, or even a Muslim TERRORIST!


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