The Volokh Conspiracy

Mostly law professors | Sometimes contrarian | Often libertarian | Always independent


How powerful are AR rifles?

About the same as other rifles


Several federal and state courts are relitigating the constitutionality of "assault weapon" bans after the Supreme Court's decision in New York State Rifle & Pistol Association v. Bruen. Under Bruen's text-and-history test, government attorneys have argued that such laws fit within a supposed historical tradition of banning what the government calls "unusually dangerous" arms; the attorneys point to not-really-on-point historical laws about weapons such as Bowie knives or slungshots (a type of flexible hand-held impact weapon).

As detailed in a pair of previous posts, the mainstream historical tradition for controversial arms such Bowie knives and slungshots was to forbid concealed carry, to restrict sales to minors (especially without parental consent), or to impose extra punishment for misuse. But not to prohibit possession or sales for adults. See the previous VC posts, The legal history of bans on firearms and Bowie knives before 1900 and Bowie knife statutes 1837-1899. Although the articles are mainly about Bowie knives, many of the quoted statutes also covered slungshots.

"Assault weapons" long have been portrayed as exceptionally powerful firearms that are far more dangerous than other modern firearms and ill-suited for lawful activities like self-defense. When enacting the nation's first "assault weapon" ban in 1989, the California legislature declared that "each firearm has such a high rate of fire and capacity for firepower that its function as a legitimate sports or recreational firearm is substantially outweighed by the danger that it can be used to kill and injure human beings."

Five federal circuit courts relied on the lethality rationale pre­-Bruen to uphold "assault weapon" bans. The First, Second, and Fourth circuits asserted that "assault weapons" have "a capability for lethality—more wounds, more serious, in more victims—far beyond that of other firearms in general, including other semiautomatic guns." The D.C. Circuit claimed that "assault weapons" like AR rifles are designed "to shoot multiple human targets very rapidly" and "fire almost as rapidly as automatics." The Seventh Circuit asserted that such firearms "enable shooters to fire bullets faster" and their "spray fire" design makes them more dangerous in mass shootings. The Fourth Circuit went so far as to hold that "assault weapons" are not protected arms under the Second Amendment because of their deadly similarity to machine guns. The First Circuit cited medical sources claiming that "assault weapons" cause far more devastating wounds that other firearms and declared that using such firearms for home defense "is tantamount to using a sledgehammer to crack open the shell of a peanut."

Thus, the prohibition argument is based on 1. Rate of fire, and 2. The power of the weapons' bullets.

The rate of fire claim is preposterous. Semiautomatic rifles as a class (including those that are supposedly "assault weapons") fire at essentially the same rate as semiautomatic handguns. These handguns, from companies such as Ruger, Smith & Wesson, Springfield, or Glock, are the most common defensive firearms in the United States; under the Supreme Court's decision in District of Columbia v. Heller, they may not be prohibited. As then-Judge Kavanaugh argued in his dissent in Heller II, it is irrational to single out semiautomatic rifles for prohibition based on rate of fire, given that semiautomatic handguns are plainly constitutionally protected. Heller v. District of Columbia, 670 F.3d 1244 (D.C. Cir. 2011) (Kavanaugh, J., dissenting).

This post will mainly discuss the second argument: that "assault weapon" bullets are much more destructive than bullets from other firearms. This post is co-authored by Campbell University law professor Gregory Wallace, who has published two articles on "assault weapons," the most recent being "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.)

As post-Bruen litigation proceeds, more absurd claims are appearing in court filings and opinions about the extreme firepower of "assault weapons" and their unsuitability for self-defense. This post discusses two such examples. The first is from the California Attorney General in Rupp v. Bonta, a case challenging California's "assault weapon" ban. It was remanded by the Ninth Circuit for reconsideration in light of Bruen and is currently pending in federal district court in California. The second is from a recent federal district court opinion in Bevis v. City of Naperville, Illinois, denying a preliminary injunction against state and local "assault weapon" bans.

The discussion below involves precise description of the wounding effects of different types of ammunition. If you don't want to read such things, that is your reasonable choice. Just don't make decisions about what arms persons under your direct or indirect control can possess if those decisions are based on wounding effects and you refuse to be informed about wounding effects.

I. The names of different rifles

Let's start with some nomenclature for firearms models. The "AR" in AR-15 stands for "ArmaLite Rifle." It was the 15th model invented by the ArmaLite company. The AR-17 (which never went very far) was a shotgun. The AR-15 was an improved version of the AR-10 of 1956. In 1959, ArmaLite sold the AR-15 patents to Colt's Manufacturing Company.

Colt's then produced two firearms lines from the patents. The semiautomatic AR-15 rifle was introduced to the civilian market in 1964. The M16 was an automatic (machine gun) version for military use; it was sold in large quantities to the U.S. military and became a standard infantry weapon during the Vietnam War. The M16 and AR-15 look the same, except that the M16 has a selector switch that allows the user to choose automatic fire. Internally, the M16 has components for automatic fire and the AR-15 does not. Today, the military has adopted an improved version of the M16, namely the M4 carbine. (A carbine is a relatively short rifle.)

Meanwhile, the patents that Colt's had bought from ArmaLite expired in 1977. Today, most rifle manufacturers make a rifle based on the AR platform. However, Colt's still owns the tradename "AR-15." So precisely speaking, none of the firearms from the other manufacturers can be called an "AR-15." This post, except when quoting or summarizing writings that incorrectly use "AR-15" when they mean a broader group of rifles, will simply use the term "AR" for the class of rifles that use the AR platform.

II. Colonel Tucker's expert declaration in Rupp

The California AG has served the Rupp plaintiffs with an expert report and declaration from retired Colonel Craig Tucker, U.S. Marine Corps, who served as an infantry officer for 25 years and commanded combat units in Iraq. The curriculum vitae attached to his report is impressive and his service appreciated. Colonel (Ret.) Tucker did not disclose in either his report or CV that he is a founding member of the Veterans Advisory Council to Michael Bloomberg's gun-control advocacy group Everytown for Gun Safety.

Describing the purported lethality of the civilian AR-15, the most popular target of "assault weapon" bans, the Tucker report states:

The AR-15 and M4 are both designed to fire a .223 round that tumbles upon hitting flesh and rips thru the human body. A single round is capable of severing the upper body from the lower body, or decapitation. The round is designed to kill, not wound, and both the AR-15 and M4 contain barrel rifling to make the round tumble upon impact and cause more severe injury. The combination of automatic rifle and .223 round is a very efficient killing system. The same can be said of the AR-15.

These five sentences are a cascade of errors and absurdities.

II.A. "The AR-15 and M4 are both designed to fire a .223 round . . ."

The Tucker declaration asserts that the M4 is "designed to fire a .223 round." In fact, the the military's M4 carbine is designed to fire the 5.56mm NATO round, not the civilian .223 Remington round. It is difficult to understand how a Marine colonel with combat infantry experience would think the M4 is designed for the .223 round.

The numbers .223 and 5.56 designate the caliber of the round based on a rough approximation of bullet diameter, which is expressed in thousandths of an inch (.223 caliber) or millimeters (5.56 caliber). The U.S. military uses the NATO designation, measured in millimeters.

While the .223 and 5.56 rounds have the same bullet diameter, there is a difference. The case for the 5.56mm has a .125-inch longer throat and thus can be loaded with additional gun powder, resulting in slightly higher performance. The military M16 and M4 are 5.56mm. Civilian guns on the AR platform are sometimes .223, but the majority are  5.56mm (still able to use .223), or other calibers. Because of the higher pressure created when fired, the 5.56 round should not be used in an AR rifle chambered only for the .223 round. The .223 round can be used in a 5.56 chamber, but may cause improper cycling (e.g., jams) with shorter barrels.

II.B. "that tumbles upon hitting flesh and rips thru the human body."

To understand why this statement is false requires an explanation of wound ballistics, the study of the effects of a penetrating projectile on living tissue. Dr. Martin Fackler, military trauma surgeon, former director of the Army's Wound Ballistics Laboratory, and the most widely-recognized modern expert on the subject, observed that "[p]robably no scientific field contains more misinformation than wound ballistics."

A firearm bullet is propelled by the expanding gas from a gunpowder explosion. Other things being equal, a bullet fired from a longer barrel will have higher velocity than a bullet fired from a shorter barrel. For example, a bullet that travels through a 16 inch rifle barrel will spend about four times longer being propelled by the expanding gas than will a bullet that travels through a 4 inch handgun barrel.

Bullets from AR rifles, like bullets from most other modern rifles, typically have about three times the muzzle velocity of common handgun bullets. Muzzle velocity is measured at the moment the barrel exits the bullet; as the bullet travels downrange, velocity declines due to air friction.

More velocity does not necessarily mean greater wound severity—a ping-pong ball and a bullet fired at the same muzzle velocity will produce very different effects on the target (terminal results).

A starting point in wound ballistics is the kinetic energy of the bullet when it strikes the target. The formula is: KE = 1/2 x mass x (square of the velocity). Other things being equal, a bullet that is twice as heavy as a different bullet will have twice the kinetic energy.

Both velocity and bullet mass contribute to kinetic energy. Rifle bullets in general strike with much higher kinetic energy than do handgun bullets, because the rifle bullets have higher velocity.

But the bullets for the most common AR calibers (.223, followed by 5.56mm) are much smaller than the bullets from many other rifles. Thus, they strike with only about a half to a third of the kinetic energy of larger caliber rifle bullets, such as .270, .30-'06, .308, .338, .444, and so on. The larger bullets not only have a greater width (i.e. caliber), they also typically are longer.

If we were in the year 1700, then the wound ballistics analysis would be at an end, since at the time all bullets had the same shape. They were spheres. That is why today a unit of ammunition is still called a "round." However, since the early 1800s, conoidal bullets have been the norm. The shape improves aerodynamic stability, so the bullet can travel further and with less loss of velocity.

Then as now, the location of impact and type of type of tissues disrupted along the bullet's path is more influential than kinetic energy, velocity, or mass. Today, the bullet's shape and construction materials are also very important.

Tissue damage from bullets comes primarily from the permanent crushing of tissue in the bullet's path. This is the permanent cavity (a/k/a permanent track).

Additionally, if the bullet is traveling fast enough, the pressure wave following the bullet can cause temporary stretching of tissue surrounding the bullet's path. This is the temporary cavity (a/k/a temporary track).

The size of the permanent cavity is proportional to the size of the bullet. The size of the temporary cavity can vary greatly, depending on the size and location of the temporary cavity on the bullet's path and the elasticity of the tissue affected.

More elastic tissue can absorb energy more easily, and is therefore much more resistant to injury from temporary cavitation. Such tissue includes muscle, lungs, skin, blood vessels and empty or hollow organs such as the stomach, bladder, or intestines.

Less elastic tissue, such as the brain, liver, kidney, and fluid-filled organs (e.g., the heart), are more likely to shatter, rupture, or tear due to temporary cavitation. Bone fractures from temporary cavitation are rare—when a bone is shattered, it usually is due to being struck by the bullet. Injuries to extremities normally come from being hit by the bullet or bullet fragments (or bone fragments if the bone is hit) rather than by temporary cavitation.

Notwithstanding Col. Tucker's claim, the bullets fired from an AR do not "tumble[] upon hitting flesh."

Bullets never "tumble" in the ordinary sense of the word. That is, they do not perform repeated 360 degree rotations horizontally or vertically. In human tissue, an intact bullet can change the angle of penetration by up to 180 degrees, meaning that the back of the bullet is now the front. The most damage occurs when the bullet has rotated 90 degrees. Then, the entire length of the intact, nondeformed bullet disrupts tissue, thus creating a larger permanent wound cavity and a larger temporary cavity.

Changes in bullet angle are called yaw. While some ballistics experts distinguish horizontal changes (yaw) from vertical changes (pitch), most use "yaw" for any change in angle.

Below, we will describe how some military ammunition, with which Col. Tucker is presumably familiar, can yaw—that is, change angle by as much as 90 to 180 degrees in human tissue. What Col. Tucker does not understand is that many civilian AR users do not choose the yaw-prone 5.56mm full metal jacket ammunition that the U.S. military uses. In fact, many AR users choose ammunition that is designed not to yaw but instead to deform.

A bullet can yaw if it stays physically intact, retaining is shape as it moves though the target. But many bullets, especially those made for self-defense, are designed not to stay intact. These bullets are designed to fragment, expand, or deform when they strike a target. For simplicity, we will call such bullets "deforming bullets," because they are designed to lose their original form when they strike.

Why is deforming ammunition often chosen for defensive rifles and handguns of all types? Why do many law enforcement agencies mandate that their deputies and officers use such ammunition? The main reason is safety.

If a bullet stays intact, there can be two results: It can just come to a stop in the body. Or it can continue through the body and exit the other side, creating an exit wound (as opposed to an entry wound).

This can be a bad result for two reasons: First, the exited bullet could hit another person. For example, when Alec Baldwin shot a victim on a movie set, the bullet entered her chest, killed her, exited, and then struck and injured a second victim. In a law enforcement or self-defense situation, the bullet that exited the criminal's body might hit an innocent victim.

Second, the purpose of shooting another person is to make that person stop doing something immediately, such as perpetrating a violent felony. Therefore, all of the kinetic energy from the bullet should be delivered to the perpetrator, to increase the possibility that the bullet will stop the perpetrator.

Deforming bullets are designed to not exit the body. Instead, they are designed to impart all their kinetic energy to a single target. Because they are made not to stay intact, they do not yaw, or to use Col. Tucker's word, "tumble."

There are many varieties of deforming ammunition, based on shape, materials, and construction. For example, in a hollow-point bullet, the tip opens up like flower petals as its moves through the target. Similarly, a solid soft tip on a bullet might flatten or "mushroom." The expansion by whatever means gives the bullet a larger diameter, which crushes more tissue; it also increases the size of both the permanent and temporary cavities. When the bullet deforms or expands, it becomes blunter and thus more stable, preventing the "tumbling" described by Col. Tucker. Such bullets also can fragment in tissue, with the fragments spreading out and creating their own permanent wound tracks separate from the main wound track. These fragments greatly increase the permanent cavity size as they tear and detach tissue displaced by the temporary cavity. A deforming or fragmenting bullet from a powerful handgun can produce similar effects to tissue, resembling those from a much faster rifle bullet.

Thus, in most situations of lawful defense of self or others, deforming/expanding bullets do the best job of increasing the likelihood that the imminent or ongoing attack will be stopped, and of reducing the risk that an exited bullet could injure a bystander.

Most rules have exceptions. One of the situations when deforming/expanding bullets might not a preferred choice for self-defense is in bear country. Some people say that a flat-nosed, non-deforming bullet is the one with the best chance of making its way through an attacking bear's massive rib cage.

Col. Tucker's declaration provides no indication that he has any familiarity with the above: namely that civilian AR users can and often do choose AR ammunition that is specifically designed not to tumble.

Instead, Col. Tucker seems to mistakenly believe that all civilians users of AR rifles use the same ammunition as does the military for the M16 and M4. That ammunition is 5.56mm FMJ (full metal jacket). In a full metal jacket, the lead bullet core is surrounded by a jacket of metal. Lead is a very soft material. On the Moh's Hardness scale of 1-10, lead is 1.5—below a fingernail (2.5), penny (3.5), or diamond (10).

With unjacketed bullets, there is substantial lead abrasion due to friction as the bullet travels down the barrel. Lead fouling degrades accuracy. In combat situations, when a soldier might have to fire hundreds or thousands of rounds with no opportunity to clean the gun, preventing lead fouling is important. Because the full metal jacket is made of harder material than lead, much less lead abrasion builds up in the gun barrel. This is one of the reasons why full metal jacket is preferred in a military context.

For bullets that do not deform, tissue damage is (relatively) minimal as long is the bullet travels point-forward. But, as described above, some rifle bullets, such as the military 5.56 round with a full metal jacket, can yaw as much as 180 degrees, increasing wound severity. In contrast, most nondeforming handgun bullets yaw at least a little, but usually not enough to cause significant additional damage.

Nondeforming bullets from any firearm also may fragment due to stress from yawing against gravity, or after striking bone. Fragmentation increases wound severity, as described above.

In short, a nondeforming round, such as the military 5.56mm with a full metal jacket, might travel intact more or less intact through a target and could hit someone else. Or it might fragment or significantly yaw, causing greater damage.

According to the California Attorney General and Col. Tucker, the .223 round begins to instantly tumble "upon hitting flesh." As explained above, many civilian .223 or 5.56mm rounds are designed not to "tumble."

Suppose we revise Col. Tucker's declaration so that it applies only to the 5.56mm FMJ rounds with which he is familiar, and not to the plentitude of AR rounds of which he apparently has no knowledge. With a corrective and vastly narrowing construction, is Col Tucker accurate? That is, is it true that the 5.56 FMJ "tumbles upon hitting flesh"? Certainly not.

Dr. Fackler found that about 85% of military 5.56mm FMJ bullets travel point-forward at least five inches before beginning to yaw. The straighter the bullet hits the target, the longer it will take to yaw after it strikes. Thus, a nondeforming full metal jacket rifle bullet can pass completely through a human target without yawing or fragmenting, leaving a small wound channel and relatively mild injury unless it strikes a vital organ, bone, or other critical structure.

The M16 and M4 have always been subjects of military controversy. On the one hand, they are much more accurate, when functioning, than their Soviet counterpart rifles, such as the AK-47 and its lineage. The AK-47 is the automatic (avtomat in Russian) rifle invented by Mikael Kalashnikov and first manufactured in 1947. Like the M16 and M4, and unlike ARs, the AK-47 is capable of automatic fire. Compared to the AK-47, American guns are more fragile in adverse conditions, such as sand storms. The Soviet guns were built to looser tolerances (how closely the parts fit together). The result is that American rifles are more accurate when clean and Soviet rifles are less affected by dust and grit.

The modern American infantry weapons have also been controversial for another reason. Compared to the rifle ammunition issued to almost all armies past and present, the 5.56mm FMJ is unusually lightweight. This is an advantage because a soldier can carry more ammunition, and thus continue fighting longer even when resupply is not available. This is same reason that in the 18th century, American long hunters, who might be out on expeditions for months, down-graded their calibers from the standard musket calibers of .60 or .75 to the .46 or .32 of the Pennsylvania/Kentucky rifles. The less the ammunition weighs, the more one can carry.

The disadvantage is the lower the ammunition weight, the less the stopping power. As explained above, any reduction in bullet weight is exactly matched by a reduction in kinetic energy.

There have been numerous reports that the military's 5.56 FMJ round has insufficient terminal effectiveness in combat. Combat veteran and military small arms expert Jim Schatz explains, "The disturbing failure of the 5.56x45mm caliber to consistently offer adequate incapacitation has been known for nearly 20 years." He describes one Special Forces (SF) mission in Afghanistan when an insurgent was shot seven or eight times in the torso with the 5.56 round, got back up, climbed over a wall, and reengaged other SF soldiers, killing a SF medic. The insurgent then was shot another six-to-eight times from about 20-30 yards before finally being killed by a SF soldier with a handgun.

Similarly, Rob Maylor, a former Australian SAS sniper, has "on several occasions witnessed bad guys being hit multiple times by 5.56mm . . . at varying ranges and then continue[] to fight." He explains that while the 5.56 round is designed to yaw and fragment, "[t]his isn't happening all the time and as a result projectiles are passing through the body with minimal damage."

Mark Bowden's bestselling book Black Hawk Down gives vivid accounts of less-than-lethal performance of the Army's green-tip 5.56mm bullet (M855) in the Battle of Mogadishu in 1993. He describes one Delta operator's rounds as

passing right through his targets. When the Sammies were close enough he could see when he hit them. . . . [I]t was like sticking somebody with an ice pick. The bullet made a small, clean hole, and unless hit happened to hit the heart or spine, it wasn't enough to stop a man in his tracks. [The operator] felt like he had to hit a guy five or six times just to get his attention.

These instances are consistent with Dr. Fackler's own findings. He recounts that

[i]n 1980, I treated a soldier shot accidentally with an M16 M193 bullet from a distance of about ten feet. The bullet entered his left thigh and traveled obliquely upward. It exited after passing through about 11 inches of muscle. The man walked into my clinic with no limp whatsoever: the entrance and exit holes were about 4mm across, and punctate. X-ray films showed intact bones, no bullet fragments, and no evidence of significant tissue disruption caused by the bullet's temporary cavity. The bullet path passed well lateral to the femoral vessels. He was back on duty in a few days. Devastating? Hardly.

Dr. Fackler further notes that "[i]n my experience and research, at least as many M16 users in Vietnam concluded that [the 5.56mm] produced unacceptably minimal, rather than 'massive,' wounds."

Like any firearm, the AR rifle in typical calibers such as .223/5.56mm, can cause serious or lethal wounds, and so can other rifles, shotguns, and handguns. 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) .223 caliber bullet, the non-deforming 5.56mm FMJ bullet, and other larger caliber bullets typically used in hunting rifles (e.g., .30-30, .308). A comparison of those profiles shows that the wounding effects of the larger caliber bullets are at least as extensive as the .223/5.56, and typically more so.

According to Dr. Fackler, the .223 Remington is "a 'varmint' cartridge, used effectively for shooting woodchucks, crows, and coyotes." Because of its smaller size, there is an ongoing debate among hunters over whether the .223 round has adequate terminal performance for taking deer or larger game. Some states ban the use of .223 caliber rifles when hunting deer and other animals larger than varmints because their rounds lack sufficient power. The ethos of hunting is to take an animal with a single fatal shot. In the views of some state game commissions, the usual AR calibers of .223 and 5.56mm are too weak; at least a .270 is required for hunting deer, antelope, or anything larger.

II.C. "A single round is capable of severing the upper body from the lower body, or decapitation."

This is the most implausible claim in Col. Tucker's report, which is made under oath and theoretical penalty of perjury. He declares that his report "is based on my own personal knowledge and experience, and, if I am called as a witness, I could and would testify competently to the truth of the matters discussed in this Report."

No one disputes that wounds from an AR rifle, like any firearm, can be fatal. That such wounds can be "capable of severing the upper body from the lower body, or decapitation" is false.

Buford Boone is the former director of the FBI's Ballistic Research Facility for 15 years and one of the world's leading authorities on internal, external, and terminal ballistics. In his expert witness rebuttal report in Rupp v. Bonta, he describes this claim as "so ridiculous that it should, and actually does, cast doubt on [Col. Tucker's] qualifications as an expert in the field of firearms, particularly as it relates to wound ballistics."

Col. Tucker offers no examples or authority to support his claim. No doubt he will be asked at deposition or trial whether he has personally witnessed a person being decapitated or having his upper body severed from his lower body by a single .223 or 5.56 round. Mr. Boone explains in his rebuttal report why it is unlikely Colonel Tucker can answer truthfully in the affirmative:

In almost 26 years of professional involvement in the field of wound ballistics, I have never heard, even anecdotally, of an incident wherein a person was decapitated or their upper body was severed from their lower body as a result of being shot by a single projectile fired from any small arm. ["Small arm" is a term of art to distinguish hand-carried weapons from larger arms, such as naval artillery.] It is notable that the .223/5.56 is on the lower end of terminal performance potential of the vast calibers available in centerfire rifles. In fact, the .223/5.56 is below the allowable minimum cartridges for deer hunting in some states. Additionally, since reading Colonel (Ret.) Tucker's supplemental report, I have shared that statement with many associates in the firearms field. All have questioned the credentials of an "expert" that would make such a claim. It is my opinion that no examples have been provided because such performance has never been witnessed.

Although perhaps never "witnessed," claims that "assault weapons" can decapitate or dismember have appeared in several media reports and at least one court opinion. They can be traced to a U.S. military report from Vietnam in 1962. Derivatively, an NPR report on the Uvalde murders in May 2022 describes the civilian AR as "designed to blow targets apart" and claims that "its bullets travel with such fierce velocity that they can decapitate a person." The NPR article links to an article in The Intercept that cites a military report describing how "Viet Cong fighters hit with the weapon were frequently decapitated and dismembered, many looking as though they had 'exploded.'" The Intercept article links to a Gawker story that quotes extensively from the military report about "how the AR-15, chambered with the same .223 ammunition that it uses today, not only killed VC soldiers but decapitated and dismembered them." In Kolbe v. Hogan, the Fourth Circuit cited the same military report to prove the extreme lethality of the civilian AR. Military testing, the court said, found that high-velocity projectiles from the AR caused "[a]mputations of limbs, massive body wounds, and decapitations."

However, as detailed above, the US military in Vietnam never used civilian ARs or .223 ammunition; the military used M16 rifles with 5.56mm ammunition.

The testing of the M16 with 5.56mm cited by the Fourth Circuit and some credulous media was conducted as part of Project AGILE, part of a research program in Southeast Asia initiated by the Department of Defense's Advanced Research Projects Administration (DARPA). At the time, the military was considering whether to replace the M14 (a Korean War gun) with the M16 as its primary combat rifle. Project AGILE supplied M16 rifles to South Vietnamese combat troops for field trials to determine whether the M16 would perform satisfactorily in combat. The subsequent report included claims of massive injuries from the M16's 5.56mm round, including two amputations and a decapitation.

These claims were never confirmed. The Army's Wound Ballistic Laboratory at Edgewood Arsenal tested the lethality of the M16 in gelatin, animals, and cadavers but could not duplicate the "theatrically grotesque wounds" reported by Project AGILE. C.J. Chivers, a Pulitzer Prize winning New York Times journalist, extensively researched the testing for his book The Gun. "No matter what they did," writes Chivers, "they were unable to reproduce the effects that the participants in Project AGILE claimed to have seen." As Chivers writes:

even the hollow-points [common for civilian use, but not military] failed to duplicate anything like the spectacular effects recorded by the Vietnamese unit commanders and their American advisors, which had subsequently been taken as fact and much used in the . . . campaign to sell the AR-15. [Recall that the "AR-15" was at first a marketing term for both the automatic M16 and for non-automatic rifles.]

The Wound Ballistic Laboratory's lethality study was kept secret for more than four decades, Chivers explains, with the result that "at the most important time, during the early and mid-1960s, the Project AGILE report, with its suspicious observations and false conclusions, remained uncontested." The M16 "continued to rise, boosted by a reputation for lethality and reliability that it did not deserve."

In other words, the military wanted to switch to the M16, notwithstanding complaints from many soldiers that it is underpowered. The military used the sensational Project Agile claims, including two purported instances of limb amputations and one of a decapitation, to counter the complaints about the M16's weak firepower. The military in fact knew that the claims from Project AGILE could not be true, because extensive testing by the Army's Wound Ballistic Laboratory had proven that the Project AGILE claims were not true. Nevertheless, the military insisted on adopting the M16 and suppressed the true facts reported by the Wound Ballistic Laboratory.

Dr. Fackler recounts that there were other claims in the 1960s and 70s that the M16's high velocity bullets caused "massive" and "devastating" injuries, but these claims were disproven or contradicted by other reports. Delegates to war surgery conferences in the early 1970s "reported no unusual problems associated with 'high-velocity' bullet wounds in Vietnam. There were no reports of rifle bullet wounds causing traumatic amputations of an extremity."

Combat veterans have rejected claims that .223 or 5.56 rounds are capable of beheading people. Delta operator Bob Keller said he has never seen anyone decapitated by an AR round and called the claim "bullshit." Rob O'Neill, the Navy SEAL who killed Osama bin Laden, said the claim is "100% inaccurate" and "there is no way, no way" that a .223 or 5.56 round can decapitate someone. "As a former Navy SEAL who has shot people up close with something similar to an AR-15, you don't blow their head off, it's not how it works." O'Neill added, "I shot bin Laden three times in the head up close with the same caliber and it didn't decapitate him."

In sum, Col Tucker's "expert" claim that a .223 round can cut a body in half is incorrect.

II.D. "The round is designed to kill, not wound . . ."

Every ordinary round—whether fired from a handgun, rifle, or shotgun—fairly can be described as "designed to kill." Some specialized rounds are marketed as "less than lethal"—e.g., rubber bullets, beanbag rounds; they typically injure and sometimes kill. No normal lead ammunition is specifically "designed to wound" and not kill. All defensive ammunition is designed to take the adversary out of the fight, and for no other purpose. The purpose can be accomplished either by killing or with a wound severe enough to incapacitate the adversary.

II.E. "and both the AR-15 and M4 contain barrel rifling to make the round tumble upon impact and cause more severe injury."

Here, Col. Tucker's claims become bizarre. Rifling is spiral grooves or other features on the inside surface (bore) of the barrel that spin the bullet on its longitudinal axis as it travels down the barrel. Within the bore, the raised parts are the lands and the flat parts are the grooves. By definition, every rifle contains rifling. So do almost all handguns. Rifling makes the bullet spin on its long axis, and improves aerodynamic stability. Rifling is not a feature unique to the AR; every rifle has rifling.

The purpose of rifling is to stabilize the bullet in flight, not to make the bullet tumble when it strikes. Tumbling (rotating end over end) is the opposite of stability. The higher the barrel's "twist" rate—how many inches a bullet must travel down the barrel to rotate one full turn—the more aerodynamically stable the bullet will be. Think of a football: the tighter the spiral, the faster, farther, and more accurately it will travel.

What of the M16? Very early select fire models of the AR-15 (before it became the M16) had a slow twist rate of 1:14; that is, in a 14 inch barrel, a bullet would rotate once. In a longer barrel, such as 24 inches, the bullet would still rotate less than twice. Due to Swedish objections about the slow twist rate, the first M16s put into service has a twist of 1:12. A misconception arose bullets with the 1:12 twist would yaw or tumble in flight. Dr. Fackler explains:

The notion that a common cause of increased wounding is the bullet's striking at large yaw angles (angle between the bullet's long axis and line of flight), or even sideways due to "tumbling" in flight is clearly fallacious. Anyone who has ever shot a rifle and observed the holes made by the bullet recognizes that they are round, not oblong, as would be the case if they yawed or tumbled in flight. This misconception seems attributable in large measure to misinterpretation of a report published, in 1967, by Hopkinson and Marshall. These authors presented diagrams of the yaw angles and patterns made by the bullet tip in flight. The angles on their drawings were exaggerated for clarity, showing 25 to 30 degrees rather than the 1 to 3 degrees that actually occur for properly designed bullets of small arms. . . . Thus bullet yaw in tissue, an important consideration, has been confused with bullet yaw in flight, which is, in most cases, of negligible consequence.

Dr. Fackler was describing what every target shooter knows from observation. Whether shooting near or far, and no matter what the gun, the holes in paper targets will be circles. Perhaps imperfect circles, with one side three degrees greater than the other. At whatever distance, a bullet through air only slightly deviates from a perfectly straight path, accounting for wind effects and gravity over distance.

During the 1960s, the fairly low twist rate of 1:12 did often result in yawing and fragmentation upon impact. These days, the military M4 has been improved with a 1:7 twist. (So in a 21 inch barrel, the bullet would rotate on is long axis three times before exiting the muzzle.) Civilian ARs today typically have twist of 1:7 to 1:9. Overall, there is no significant bullet yaw or pitch during flight, regardless of gun. If any occurs after penetration, that is due to the matter encountered, rather than the rifling of the gun.

Finally, Col. Tucker claims that the rifles he is denouncing (AR-15, M4) are designed for offensive combat, not self-defense:

I carried my M4 for offensive combat and a handgun for self-defense. Defensive combat is generally up close and very personal. At that range, it is very difficult to use a rifle as a defensive weapon, except as a blunt force instrument.

This will come as great surprise to the many millions of Americans who have relied on a rifle as their primary home defense arm. Granted, rifles are less maneuverable than handguns at very close quarters; even so, rifles are more accurate because they are easier to aim, more stable when held, and have longer barrels. The AR in particular has low recoil, making it easier for users with limited upper body strength to control. As explained in a pro/con article by Guncraft Training Academy, one of the advantages of an AR rifle compared to a handgun is that the AR bullet is much smaller than typical defensive handgun rounds. Hence, the bullet loses velocity sooner than does a bigger bullet when it strikes the target. Therefore, the AR bullet is less likely to over-penetrate—that is, to exit the criminal's body and thereby endanger other people.

III. The Bevis v. City of Naperville opinion

The federal district court opinion in Bevis v. Naperville offers a preview of how Bruen-defying lower courts will uphold "assault weapon" bans. The Bevis Judge, Virginia M. Kendall, had previously held that Chicago's ban on all public firing ranges in the city did not violate the Second Amendment. Ezell v. City of Chicago, 2010 WL 3998104 (N.D. Ill., Oct. 12, 2010). That decision was later reversed by the Seventh Circuit. 651 F.3d 684 (7th Cir. 2011).

In Bevis, Judge Kendall declared that "[a]ssault weapons pose an exceptional danger, more so than standard self-defense weapons such as handguns." She cited in support the Second Circuit's pre-Bruen assertion in New York State Rifle & Pistol Ass'n v. Cuomo that "these weapons tend to result in more numerous wounds, more serious wounds, and more victims." These claims are incorrect.

III.A. Rate of fire: "more numerous wounds . . . more victims"

Like the pre-Bruen circuit courts, the Judge Kendall first addressed the banned firearms' rate of fire; they "fire quickly," she said. Civilian semiautomatic-only "assault weapons" are not machine guns; they fire only one round for each pull of the trigger. While Judge Kendall initially claimed that an "assault weapon" can empty a 30-round magazine in six seconds, she conceded that a more realistic rate of fire is one round per second. At that rate, however, "assault weapons" are no more dangerous than handguns, from which an average shooter typically can fire two or three rounds a second.

III.B. Terminal effects: "more serious wounds"

Judge Kendall then described the supposedly massive wounds that "assault weapons" produce when their bullets strike, something also emphasized in the pre-Bruen circuit court decisions. She briefly addressed two factors—muzzle velocity and bullet penetration—to show that "assault weapons" produce more devastating wounds than other firearms. Their bullets "hit fast and penetrate deep into the body," she said.

III.B.1. Muzzle velocity

To support the first factor, the Judge Kendall claimed the muzzle velocity of an "assault weapon" is "four-times higher than a high-powered semiautomatic firearm." That claim is untrue, unsupported by the cited authority, and nonsensical. Of course rifles in general have higher velocity than handguns in general, because rifles definitionally have much longer barrels. Most handgun barrels are six inches or less; rifle barrels are, by federal law, at least 16 inches. (Rifles with shorter barrels require special registration and taxation by the Bureau of Alcohol, Tobacco, Firearms, and Explosives, pursuant to the National Firearms Act of 1934).

To say that a given rifle has greater velocity than handguns is true, but this is not in any way unique to AR rifles.

The muzzle velocity of a 55-grain .223/5.56 round from an AR is around 3200 feet-per-second (fps), while larger-caliber rounds used in hunting and other types of rifles have muzzle velocities from 2500-3000 fps. Popular 9mm, .40, and .45 caliber handgun rounds typically have muzzle velocities from 1000-1200 fps. So do most 40-grain .22 caliber rimfire long rifle (LR) rounds. (The puny .22LR is popular for both rifles and handguns; its low power makes it an excellent choice as a child's first firearm.)

At most, the muzzle velocity of an "assault weapon" is three times that of lower-velocity semiautomatic handgun round.

Judge Kendall cited an article by Dr. Peter Rhee et al. to support the "four-times higher" claim. Muzzle velocities of various firearms do not appear on the cited page (855), but do in two charts on the next page (856). Nothing in the charts or the text states or supports the "four-times higher" claim; in fact, the muzzle velocities in the article reflect those set out above. It is unclear where the judge came up with the "four-times higher" figure.

Not only is Judge Kendall's claim wrong and unsupported, it is nonsensical. She declares that the banned weapons fire four-times faster than a "high-powered semiautomatic firearm." Ban advocates and the media often refer to semiautomatic "assault weapons" as "high-powered." In target rifle competitions, all calibers above the diminutive .22 are called "high power." So competitors using a .22 rifle would compete in one class, and competitors with larger rifles would compete in a different class.

The Rhee article defines "high-velocity" bullets as those with a velocity of at least 2500 fps, while "low-velocity" bullets travel at 1200 fps or less. If an "assault weapon" and a "high-powered semiautomatic firearm" are one in the same, any comparison between the two is nonsensical.

Judge Kendall's reliance on bullet velocity to prove "assault weapons" are exceptionally dangerous misunderstands the fundamentals of wound ballistics. Her claim is really just an observation that rifles in general are more powerful than handguns in general.

II.B.2. Wound damage

While "assault weapon" bullets typically "penetrate deep into the body," Judge Kendall accurately noted, so do handgun bullets. FBI testing shows that to be reliably effective, handgun bullets must penetrate soft body tissue 12-to-18 inches, a range necessary to reach and disrupt a vital organ in a human target.

Judge Kendall offered a description of the wounding effects of "assault weapon" bullets to depict them as highly dangerous. Rather than citing scholarly articles on wound ballistics or quoting wound ballistics experts or military trauma surgeons who regularly treat rifle wounds, she relied on an NPR report and an opinion article in The Atlantic

The NPR report was published following the Uvalde, Texas, murders. Judge Kendall quoted one doctor from the article who describes bullets from "assault weapons" as causing "cavitation" in which the projectile creates a "large cavity." But both handgun and rifle rounds can cause large temporary cavities. Dr. Fackler notes that "[t]emporary cavitation is not a modern phenomenon associated exclusively with projectiles of high velocity." He describes the temporary cavitation caused by common handgun rounds. All centerfire rifle bullets (that is, every modern round bigger than above the .22 rimfire) and large handgun bullets often cause a large temporary cavity. The size of the cavity can vary considerably, depending on the tissue in which it forms. The NPR doctor's quote describes a common characteristic of handgun and rifle wounds; it does not describe anything exceptional about "assault weapons."

Judge Kendall also quoted an op-ed in The Atlantic by a radiologist who viewed AR wounds from the Parkland shooting from her computer screen. Supposedly, the bullet "does not actually have to hit an artery to damage it and cause catastrophic bleeding."

While it is not impossible for the temporary cavity to tear a hole in an artery, it is rare. Dr. Fackler explains that "[b]lood vessels are usually simply pushed aside and are almost never disrupted by temporary cavitation." He observed one case in which the temporary cavity created by an expanding handgun bullet tore a hole in the aorta at its junction with the right renal artery. He writes, "I must emphasize the extreme rarity of this case. I never published it, however, not wishing to add to the widespread wildly exaggerated effects attributed to the temporary cavity by many" (original emphasis).

The Atlantic writer further claimed that "[e]xit wounds can be the size of an orange."

Assertions that .223/5.56 rounds create huge exit wounds often appear in media accounts. One radiologist calling for "common sense gun reform" claimed that "exit wounds associated with AR-15 firearms are often the size of grapefruits." Rep. Lucy McBath (D-Ga) declared on Twitter that "[w]ith assault rifles, exit wounds can be a foot wide," as did a trauma surgeon with military experience quoted in the New York Times. That same doctor offered this hyperbolic description in another media interview:

[A]s they travel through the body, [AR bullets] will destroy all the organs in the region of where they're traveling, and that's really due to the kinetic energy that those bullets impart. So, any centrally-fired weapon, if it hits anywhere in the central portion of the body, will blow a huge hole in a human being, particularly the exit wound, and it'll almost always be lethal. . . .

The average size of a navel orange, the most popular orange in the U.S., is three inches across, although some can grow as big as 4.5 inches in diameter. The average size of a grapefruit is four-to-six inches.

Studies have measured exit holes of .223/5.56 rounds in both gelatin testing and actual autopsy analysis. One study, using ballistic gelatin, found that the size and position of the temporary cavity influenced the size of the exit wound for 5.56mm NATO FMJ round. Testing showed that the exit hole reaches its maximum size if the bullet exits when the temporary cavity is at its maximum. The average size of the exit hole when the temporary cavity was maximized was 2.4 inches.

Another study examined 27 forensic autopsy records from persons shot with 5.56mm ammunition during dispersion of a mass protest in Bangkok in 2010. Twenty-three had typical entrance wounds. Exit wounds were various sizes and shapes, depending on the degree of bullet yaw and whether the bullet exited during the largest part of the temporary cavity. The six largest exit wounds in this group were two stellate (star) shape in the skull measuring 2.4 x 1.8 inches (6 x 4.5 cm) and 1.9 x 1.2 inches (5 x 3 cm), one stellate shape entering the back and exiting the abdomen measuring 1.2 x 1 inches (3 x 2.5 cm), one oval shape in the abdomen exiting in the lower back measuring 0.8 x 0.4 inches (2 x 1 cm), one oval shaped entering the back and exiting the chest measuring 0.8 x 0.4 inches (2 x 1 cm), and one stellate shape in the face exiting the neck measuring 0.6 x 0.4 inches (1.5 x1 cm). The remaining 17 bullets in this group either exited the body without yaw, fragmented, or left no exit wounds at all. Exit wounds were small round or oval shapes measuring less than 0.4 in (1 cm).

Nine persons suffered atypical entrance wounds from bullets that destabilized before hitting the body either by ricochet or hitting an intermediate target, causing the bullets to enter the body either sideways or at an angle. One entered the skull with the resulting exit wound having stellate shape measuring 2.9 x1 inches (7.5 x 5 cm). Another entered the lateral chest and exited the anterior chest with a stellate shape measuring 2.75 x 2.4 inches (7 x 6 cm). Two others hit extremities, one in the forearm and the other in the thigh, both with oval shaped exit wounds measuring 1.5×0.8cm (0.6 x .3 cm) and 1.2 x 0.7 cm (0.5 x 0.3 in), respectively. Of the remaining five, two caused head lacerations but did not enter the skull and three had no exit wounds, but retained the bullet or bullet fragments.

None of the exit wounds in either study are the size of oranges or grapefruits.

Such misreporting is nothing new. Thirty-three years ago, Dr. Fackler described how media accounts embellished the injuries suffered by five children murdered in the 1989 elementary school shooting in Stockton, California, one of the first modern mass shootings; the crime created the national "assault weapon" controversy. Dr. Fackler did ballistics testing on the ammunition used in the criminal's semiautomatic AKM-56S rifle, whose rounds are larger than the .223/5.56mm rounds that are most often used in ARs. Dr. Fackler also reviewed the autopsies of the children killed. He explained:

Much of the media coverage generated by the Stockton shooting has contained misstatements and exaggerations. The myth of "shock waves" resounding from these "high velocity" bullets "pulverizing bones and exploding organs" (even if they were not hit by the bullet) "like a bomb" going off in the body was repeated by the media, in certain cases even after they were furnished solid evidence that disproved these absurdities. None of the autopsies showed damage beyond the projectile path. One "expert" was quoted as stating that the death rate from "assault weapons . . . approaches 50[%]." Another, reporting on the effects of "high speed" bullets, stated that "most of those hit in an extremity will end up with amputations. If you're hit in the trunk, it becomes a lethal injury. . ." In the Stockton schoolyard, the death rate was 14% and none of the [wounded] victims died later or required extremity amputation.

Judges should think twice about relying on unsworn, anecdotal, and hyperbolic statements gleaned from media articles produced by gun prohibition advocates.

III.B.3. "the injury along the path of the bullet from an AR-15 is vastly different from a low-velocity handgun injury."

This statement is generally correct, but can be misleading without more context. Rifle bullets typically do more damage to tissue than handgun bullets, but not always so, depending on where the bullets strike. A handgun round to the brain, spinal cord, heart, or other vital organ almost always will cause more serious damage than a rifle round to an extremity or other non-vital part of the torso. As Dr. Rhee explains, "[m]ost experienced trauma surgeons will testify that what part of the body is hit by [the] gun is more important than the size of the gun."

To classify a firearm as exceptionally lethal, there must be a baseline for comparison. Ban advocates and some courts attempt to make "assault weapons" like the AR seem unusually dangerous by comparing them to handguns, as seen in the quote above. The AR does fire higher-velocity bullets that impact with much greater force than handguns, but that is true of virtually all rifles. That handguns generally are less terminally effective than rifles is nothing new. But comparing the effects of AR bullets to handgun bullets to prove the exceptional lethality of "assault weapons" is like comparing a Prius to a Model T to prove the Prius is much faster than average automobiles.

Media articles that describe massive wounds from "assault weapons"—such as the ones quoted above—almost never describe or compare wounds caused by larger-caliber rifles or shotguns. The AR's wounding power is no more devastating than common hunting rifles, and typically less so (partly because its bullets are smaller). 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." Dr. P. K. Stefanopoulos, trauma surgeon and former career military officer who has written extensively on wound ballistics, confirms that at distances of less than ten feet "the shotgun produces the most devastating injuries of all small arms."

We agree that AR rifles, like every firearm, are dangerous when misused. The notion that AR rifles are unusually powerful compared to other rifles is false. Wounds caused by the AR typically are not more serious or lethal than wounds caused by larger-caliber hunting rifles, shotguns, and even some powerful handguns. These are demonstrable facts, supported by genuine firearms and wound ballistics experts.

This post was updated on March 20, 2023, for technical corrections in the last paragraph of II.A. and the history of twist rates in II.E.