The Volokh Conspiracy
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AR rifle ammunition is less powerful than most other rifle ammunition
Bullet speed matters, but so does bullet weight
According to "assault weapon" ban proponents, the AR rifle's lethality is all about how fast its bullets travel. The Washington Post recently claimed that "what makes [the AR] so deadly is the speed of [its] bullet." "The higher speed of a bullet from an AR-15 causes far more damage after it hits the body and drastically reduces a person's chances of survival." Scott Pelley at CBS News declared that "the AR-15's high velocity ammo is the fear of every American emergency room." In a March 2023 order denying a motion for a preliminary injunction in Delaware State Sportsmen's Ass'n v. Delaware Dep't of Safety and Homeland Security, Judge Richard Andrews described how "intermediate-caliber rounds fired at high velocity" cause "catastrophic" wounds with "multiple organs shattered, bones exploded, soft tissue absolutely destroyed, and exit wounds a foot wide."
President Joe Biden repeatedly has exaggerated the velocity of AR bullets, most recently asserting that they travel five times as fast as handgun bullets. To prove that AR's pose an "exceptional danger," Judge Virginia Kendall claimed in her February 2023 order denying a preliminary injunction in Bevis v. Naperville that "[t]he muzzle velocity of an assault weapon is four times higher than a high-powered semiautomatic firearm."
This post will discuss the comparative velocity and kinetic energy of AR bullets and how those factors affect bullet penetration and wound severity. It is co-authored by Campbell University law professor Gregory Wallace, who has published two articles on "assault weapons," most recently "Assault Weapon" Lethality, 88 Tenn. L. Rev. 1 (2020). Professor Wallace and I are among the co-authors of the law school textbook Firearms Law and the Second Amendment: Regulation, Rights, and Policy (3d ed. 2022, Aspen Pub.). In an earlier post, we examined false claims that the AR type rifles are exceptionally powerful.
While AR rifles can be chambered in various calibers, they most commonly fire the .223 Remington and 5.56 NATO rounds. The numbers .223 and 5.56 designate the caliber of the round based on a rough approximation of bullet diameter, which is expressed in decimals an inch (.223 caliber = 223 thousandths of an inch; .45 caliber = 45 hundredths of an inch ) or millimeters (5.56 caliber). The U.S. military uses the NATO designation, measured in millimeters. As detailed in our previous post, the .223 and 5.56 are mostly interchangeable.
- Understanding terms
"AR" is short for "ArmaLite Rifle," inventor of the firearm in the 1950s. "AR-15" is the name for a particular model by Colt; the AR-15 is a now shrinking minority among AR type rifles, since the patents have long expired.
Like the vast majority of modern rifles, the AR fires "high velocity" bullets, whereas most modern handguns fire "low velocity" bullets. Bullet velocity is measured at various distances, since velocity declines as a bullet travels downrange. The highest velocity is the instant the bullet leaves the barrel of the gun and exits the muzzle. The velocity at that point is called "muzzle velocity."
There is no scientific or industry definition of "high velocity." American researchers who assign numerical values to the term generally use "high velocity" to refer to bullets with a muzzle velocity of at least 2,500 feet per second (fps), and "low-velocity" for bullets with a velocity of 1,200 feet per second or less.
Other things being equal, greater velocity increases a bullet's striking power. So does increasing the mass of the bullet. The overall striking power is commonly known as "kinetic energy" and is measured in foot pounds (a force of one pound moving through a distance of one foot). The formula for kinetic energy is one-half times bullet mass times velocity squared (KE = 1/2mv2).
As we detailed in How powerful are AR rifles?, a bullet's impact on a human target is also influenced by the shape and composition of the bullet and where the bullet strikes. Our article refuted false claims from the early 1960s (which are still repeated by low-information journalists today) that the AR bullets have greater wounding effects than other rifle bullets.
In this post, we provide data about the velocity kinetic energy of AR ammunition compared to other ammunition. We also address the false claim that AR ammunition has some supposedly unique ability to penetrate body armor or interior walls.
2. Identifying velocity and kinetic energy values for various firearms
The following chart lists the typical velocity and kinetic energy of modern handgun, rifle, and shotgun projectiles measured at the firearm's muzzle. Values in the chart are supplied from Cartridges of the World (17th ed. 2022) and manufacturer websites. Common AR-15 rounds (.223 and 5.56) are bolded.
For most of these calibers, Cartridge of the World lists ammunition from a variety of manufacturers, each with its own performance characteristics. The figures below are neither the high end nor the low end for any given caliber. For weight in grains, 7,000 grains = 1 pound. An appendix at the end of this post provides a short description of when a given cartridge type was invented, its most common uses, and the kinetic energy range of various cartridges in a given caliber.
(U.S. Army standard through 1983)
|5.56 NATO (U.S. standard since 1984)||62||3100||1325|
|.300 Win Mag||165||3200||3753|
|.338 Win Mag||250||2700||4048|
|.338 Lapua Mag||250||2970||4896|
|.458 Win Mag||350||2500||4859|
|12-ga shotgun slug||438||1610||2521|
3. Comparing the AR's velocity and energy
The AR does not fire bullets four or five times faster than handguns, as claimed by President Biden and Judge Kendall. The AR bullets are about three times faster than common 9mm handguns and only a little more than twice as fast as more powerful handguns (.357 and .44 magnums).
The apples-to-apples comparison is with other centerfire rifles. All the rifle cartridges listed above are centerfire, except for the .22LR. In a centerfire cartridge, the primer is in the center of the base of the cartridge; in a rimfire, the primer is inside the rim of the cartridge base. Centerfire cartridges are generally more powerful. Rimfire cartridges above .22 caliber are not very common these days.
As the above chart indicates, bullet velocity among popular centerfire calibers ranges from 2450 to 3250 fps, which is 75 to 100 percent of the AR's speed. (The only exception is the .300 Blackout, which is effective only at short ranges). Thus, other centerfire rifles fire bullets at speeds as fast or almost as fast as the AR-15.
The starkest difference between AR bullets and other rifle bullets is seen when comparing kinetic energy values. As with all centerfire rifle bullets, AR bullets strike with much higher kinetic energy than handgun bullets. But among rifle bullets, the .223 and 5.56 bullets strike with much less kinetic energy, despite their higher velocity. This is due to their smaller bullet size. For example, common hunting caliber bullets (.270, .308, .30-06) strike with around twice the energy of AR bullets. Larger rifle bullets (.300 Win Mag, .338 Win Mag, .338 Lapua Mag) strike with three or more times the energy of AR bullets.
A favorite tactic of "assault weapon" ban proponents is to compare AR bullet velocity to handguns to prove that the AR is far more dangerous than other semiautomatic firearms. What they don't tell you is that all centerfire rifle bullets travel at much higher speeds than handgun bullets and that AR bullets impact with much less force than most other centerfire rifles. Comparing the higher speed of AR bullets to handguns to prove ARs are exceptionally dangerous is deceptive.
The tactic is like comparing the running speed of a particular dog breed to the speed of an average housecat. Most dogs are faster than most cats. However, showing that a particular breed of dog is faster than a cat does not prove that the particular breed is much faster than other dog breeds.
4. Bullet velocity, energy, and wounding power
Higher bullet velocity does not necessarily mean greater wound severity. A ping-pong ball and a rifle bullet fired at the same velocity will produce very different terminal results. According to military trauma surgeon Dr. Martin Fackler, former director of the Army's Wound Ballistics Laboratory, and the most widely-recognized modern expert on the subject, "The false belief that a bullet damages tissue in direct proportion to its velocity is widespread." Dr. P.K. Stefanopoulos, trauma surgeon and former career military officer who has written extensively on wound ballistics, confirms that "current thinking suggests that the impact velocity can be misleading as the sole indicator of the extent and severity of the inflicted wound." ("Impact velocity" is the bullet's velocity as the moment the bullet strikes the target. Due to air friction from travel downrange, impact velocity is always lower than muzzle velocity, unless the muzzle is touching the target.)
While a bullet's speed can affect wound severity, it is not the only or even best measure. Compare the wounding effects of 00-buckshot from a 12-gauge shotgun, a .44 caliber Magnum hollow point bullet, and .22 caliber rimfire bullet—all three fired from a distance of about 15 feet. The shotgun will cause far more tissue disruption than the .44 Magnum handgun, and the .44 Magnum handgun will cause far more disruption than the .22 rifle, despite the fact that all three have approximately the same muzzle velocity.
How bullets injure and kill has less to do with velocity and kinetic energy than with the location of impact, the bullet's physical characteristics (mass, shape, construction), and the type of tissues disrupted along the bullet's path. As we explained in an earlier post discussing the dynamics of wound ballistics, the AR certainly can cause lethal wounds, but larger caliber rifles can create more massive wounds. Especially lethal are shotguns at shorter ranges.
Wound profiles from the Army's Wound Ballistics Laboratory illustrate the permanent and temporary cavities, penetration depth, deformation, and fragmentation of both the deforming (soft point) AR .223 caliber bullet, the non-deforming 5.56mm full metal jacket (FMJ) bullet, and other larger caliber bullets typically used in hunting rifles. A comparison of profiles for AR bullets with the wound profiles for larger-caliber hunting and competition rifle bullets, such as the .243, .30-30, and .308, shows that the wounding effects of the larger-caliber bullets are at least as extensive as the .223 and 5.56 bullets, and typically more so.
At shorter distances, the shotgun produces the most devastating injuries, even though the velocity of its rounds is about the same as handgun bullets. Dr. Fackler observes that at close range "the [twelve-gauge] shotgun (using either buckshot or a rifled slug) is far more likely to incapacitate than is a .223 rifle. The shotgun is simply a far more powerful weapon."
A shotgun "slug" is a single large piece of lead. Slugs are commonly used for hunting of land animals, especially in New Jersey, where rifle hunting is not allowed. The majority of shotgun users do not use slugs. Instead, their ammunition consists of a number of pellets ("shot"). For the smallest shot sizes, such as those used for dove hunting, a shot pellet might be about the size of a grain of pepper; a shot shell for doves has about 250 to 380 pellets. For larger animals, such as deer, "buckshot" is the standard. A single buckshot cartridge contains about 8 to 12 pellets, each of them with a diameter of .24 to .36 inches. (The larger the pellet, the fewer that will fit in a shotgun shell.)
In other words, a shotgun with a buckshot can instantly unleash eight or more pellets, each of them with the same diameter as a common handgun or rifle bullet. A short range, the effect is devastating, and far more so than a single bullet from a rifle or handgun. Shotgun pellets, being spheres, have lower aerodynamic stability than do conoidal rifle or handgun bullets; hence a shotgun is not effective at long ranges.
Gun prohibitionists spread an additional falsehood: that the AR is more dangerous than other firearms because its high-velocity bullets pose a greater risk of penetrating body armor or of overpenetrating the interior walls of a building. For example, relying on the state's brief, Judge Andrews in Delaware State Sportsmen's Ass'n v. Delaware Dep't of Safety and Homeland Security stated:
The power and velocity of assault rifle bullets pose a particularly high risk to law enforcement officers. Although the body armor typically issued to law enforcement officers protects against most handgun bullets, it is not designed to withstand the high-velocity bullets described above; assault rifles therefore "readily penetrate" such body armor.
But this is true of all centerfire rifles. Soft body armor worn by police only stops rounds from handguns and shotguns. Stopping rifle rounds require steel, ceramic, or composite hard plates, which are bulky and heavier. Anti-rifle plates are typically worn by soldiers or special tactics law enforcement units. Judge Andrews' point shows one way rifles can be more dangerous than handguns, but it does not explain why the AR or other "assault weapons" are themselves exceptionally lethal "far beyond" other rifles.
Federal courts also have claimed that "assault weapons" are more dangerous than other firearms because their bullets can penetrate walls and endanger people on the other side. The Fourth Circuit in Kolbe v. Hogan twice emphasized that the banned weapons "pose a heightened risk to civilians in that rounds from assault weapons have the ability to easily penetrate most materials used in standard home construction, car doors, and similar materials." Citing Kolbe, the First Circuit in Worman v. Healey declared that "unlike the use of handguns . . . . the use of semiautomatic assault weapons implicates the safety of the public at large. After all, such weapons can fire through walls, risking the lives of those in nearby apartments or on the street." What Kolbe implies, Worman makes explicit: "assault weapon" bullets penetrate walls, but handgun bullets do not.
That is plainly false. Nearly all handgun, rifle, and shotgun rounds will pass through walls. FBI testing indicates that to be reliably effective, bullets must penetrate soft body tissue 12-18 inches, a range necessary to reach and disrupt a vital organ in a human target. This penetration capability also means that bullets will penetrate walls if the shooter misses the target.
Contrary to Kolbe and Worman, handgun rounds will penetrate several layers of sheetrock as well as exterior house walls. The difference between handgun and rifle rounds is how they behave when passing through walls. A pistol round typically remains relatively stable, while the AR's longer and thinner .223/5.56-caliber round is likely to fragment or to lose stability and tumble end-over-end (keyhole), losing energy rapidly due to the larger surface area hitting the drywall.
Therefore, .223/5.56 bullets generally penetrate less through building materials than do common handgun and shotgun rounds. This is one reason law enforcement officers often use the select-fire M4 or semiautomatic AR for raiding buildings and hostage situations, especially in urban areas.
While some bullet designs can reduce penetration through walls, the best way to minimize the chances of hurting innocent persons is to make accurate hits on the target. Because handguns require more skill to fire accurately than rifles, they typically pose a greater risk to public safety from bullet over-penetration than does the AR.
In short, the AR's high-velocity bullets have no more capability to penetrate soft body armor than do other centerfire rifles. Handgun and shotgun rounds typically penetrate building materials more than do AR rounds.
6. Summing up
Disinformation about the lethality of the civilian AR is widespread in media reports, court filings, and judicial opinions. The facts do not support claims by gun control advocates and some judges that high-velocity bullets from "assault weapons" like the AR are exceptionally dangerous or lethal. The AR rifle's bullet can cause more serious wounds than a handgun, but such wounds typically are no more severe than those caused by projectiles fired from shotguns or larger-caliber hunting rifles. The AR bullet normally penetrates less through walls than common handgun and shotgun rounds, reducing the risk to public safety from bullet over-penetration. While the AR's high-velocity bullet can penetrate soft body armor worn by law enforcement officers, almost every centerfire rifle bullet has that capability. In short, the AR's high-velocity bullet makes it a lethal weapon, but not more so than other centerfire rifles.
Appendix: Background about various cartridges
All information and quotes are from Cartridges of the World, 7th ed., except as noted.
9mm Luger. Introduced 1902. Today, "the most widely used cartridge in the United States." KE range 294 to 465.
.357 Magnum. Introduced 1935 by Smith & Wesson, revolvers. At the time, the most powerful handgun load. "It is considered the best all-around handgun hunting cartridge." KE = 400 to 644.
.40 S&W. Introduced 1989. Pistol load designed for self-defense. KE = 363 to 524.
.45 ACP. Invented 1905, put to use in the venerable and still-popular Colt 1911 pistol. Widely adopted by militaries around the world. More popular for target shooting than for hunting. KE = 244 to 534,
.22 LR (long rifle). Invented 1887. The "most popular match cartridge in existence, and also the most widely used small game and varmint cartridge." Cartridges of the World does not supply ballistic data for rimfire. We used the manufacturer's data for the CCI Standard Velocity 40 grain.
.223 Remington. Invented 1957, for the AR. "Practically every manufacturer of bolt-action rifles has at least one model chambered for the .223." KE = 965 to 1460.
5.56 NATO. Invented for the AR in 1960. A new version, adopted in 1984, has a 62 grain bullet instead of 55 grain; the KE at the muzzle is the same, namely 1325.
.243 Winchester. Invented 1955. Very common, "probably chambered in more different rifles than any other cartridge." Especially suited for deer. KE = 1599 to 2033.
.260 Remington. Introduced 1996. Very good for long distance target shooting. Good for hunters who want low recoil, but only powerful enough for big game with premium loads. KE = 2264 to to 2459.
6mm Creedmoor. Introduced 2007 and named for the NRA's iconic (in the 19th century) shooting range on Long Island. Popular for long distance precision shooting. KE = 3000 to 3700.
6.8 SPC (Special purpose cartridge). Introduced 2003 for US special forces, although not officially adopted. Attempts to solve the weaknesses of the 5.56mm in incapacitating an enemy. KE = 1444 to 2002.
.270 Winchester. Invented in 1925, it was the best long range American hunting cartridge to date. It is an adaptation of the standard U.S. Army rifle cartridge of the time, the .30-'06. KE = 2448 to 3045.
.30-.378 Weatherby. Invented in the 1950s under a U.S. Army contract. Used for very long range target shooting (e.g., 1,000 yards). Perhaps "the ultimate long-range hunting" cartridge for "for smaller species." KE = 4310 to 4840.
.300 Blackout. Invented 2009. Comes in both subsonic and supersonic loads, so the KE range is large: 498 to 1598.
.308 Winchester. Introduced 1951, sporterized version of the NATO 7.62x51mm. Excellent accuracy makes it popular for target shooters. Well-suited for big game smaller than moose or brown bear. KE = 2429 to 2759. (Plus subsonic variants of 480 or 538.(
.30-06. Adopted 1906 as the standard U.S. Army cartridge. Derived from an 1895 Winchester cartridge. "[T]he most flexible, useful, all-around big game cartridge available to the American hunter." KE = 2033 to 3076.
.30-30 Winchester. Introduced 1895. It "has long been the standard American deer cartridge." Not appropriate for over hunting shots over 200 yards. KE = 1394 to 2045.
.300 Winchester Magnum. Introduced 1963. A "magnum" cartridge has more gunpowder than ordinary loads. For long range big game. Heavy recoil. KE = 3054 to 4187.
.338 Winchester Magnum. Introduced 1957. Designed for the heaviest big game. KE = 3518 to 4164.
.338 Lapua Magnum. Development began in 1983. For snipers and very heavy game. Shoots well even at 1500 meters. KE = 4388 to 5223.
.416 Weatherby Magnum. Introduced 1989. Made for large and dangerous game. KE = 5997 to 6477.
.458 Winchester Magnum. Introduced 1956. Made for the heaviest African game. Adapted for North American use with lighter cartridges, which account for the low end of the KE range: 2938 to 5084.
.50 BMG (Browning Machine Gun). Invented 1918 for the U.S. Army and still in use by them. Sporting use in very long distance target shooting, sometimes up to 2 miles. Not very easy to carry, as weight is 20 pounds or more. KE = 12408 to 13421.
Shotgun caliber is measured in "gauge." The smaller the number, the wider the gun's bore. Among the most common gauges in the U.S. today are 12, 16, 20, and 28. Cartridges of the World does not provide shotgun ballistics. We used the manufacturer's data for the Federal Power-Shok Rifled Slug 12 Gauge 438 Grain.