Are AR-15s and magazines capable of holding more than 10 rounds of ammunition examples of arms “in common use for lawful purposes” and, therefore, protected by the Second Amendment? Or do they represent “dangerous and unusual weapons” that can be banned by governments?

New data gleaned from the largest-ever survey of gun owners is more evidence the former is true.

The National Firearms Survey, conducted in 2021 by Georgetown professor William English and updated earlier this year, queried 16,708 gun owners across all 50 states to find out, among other things, just how much AR-15s and so-called high-capacity magazines have permeated the civilian market.

The survey found that “30.2% of gun owners, about 24.6 million people, indicated that they have owned an AR-15 or similarly styled rifle.” It then asked how many of those rifles each respondent owned, finding an average of 1.8 rifles per reported owner, with the median owner having owned just one.

“This suggests that up to 44 million AR-15 styled rifles have been owned by U.S. gun owners,” English wrote.

Respondents were also asked for what purpose they owned an AR-15, with nearly two-thirds of owners citing home defense and recreational target shooting—the two most commonly cited reasons.

As for ammo magazines, 48.0% of gun owners said they’ve owned one that holds more than ten rounds. That suggests that roughly 39 million adults in the U.S. over the age of 18 have owned a “high-capacity” magazine, according to English.  He estimates that U.S. gun owners have owned up to 269 million handgun magazines that hold over 10 rounds, and up to 273 million of such rifle magazines. As with ARs, home defense and recreational target shooting were again the two most common reasons indicated for owning the magazines.

The survey data provides fresh insight into the central question at issue in the debate over the legality of “assault weapons” bans and magazine capacity limits.

Standards for each vary by jurisdiction, but almost all assault weapons laws are expressly aimed at banning the sale of AR-15s and similar rifles. Likewise, magazine restrictions almost uniformly limit civilians to ten rounds (Colorado is the only state that currently defines “large capacity” as greater than 15 rounds).

The bans have become increasingly politically salient in recent months, particularly after a string of high-profile mass shootings earlier this summer. Public support for the bans ticked up in a recent poll, and the House of Representatives was able to pass the first federal ban in nearly three decades.

At the same time, gun-rights groups have gone on the offensive in states across the country to challenge similar bans at the state and local levels now that the Supreme Court has set a roadmap for how they should be evaluated.

In Heller, the Supreme Court found that the Second Amendment protects arms “typically possessed by law-abiding citizens for lawful purposes.” The court further clarified the scope of this protection by drawing on the 1939 decision in United States v. Miller, stating “Miller’s holding that the sorts of weapons protected are those ‘in common use at the time’ finds support in the historical tradition of prohibiting the carrying of dangerous and unusual weapons.”

As for the appropriate legal test for reviewing each specific Second Amendment challenge, Justice Thomas was quite explicit in his Bruen opinion.

“When the Second Amendment’s plain text covers an individual’s conduct, the Constitution presumptively protects that conduct,” Justice Thomas wrote. “The government must then justify its regulation by demonstrating that it is consistent with the Nation’s historical tradition of firearm regulation. Only then may a court conclude that the individual’s conduct falls outside the Second Amendment’s ‘unqualified command.’”

In evaluating modern bans on AR-15s and magazines capable of holding more than ten rounds, judges will be looking at whether such items constitute weapons “in common use” and whether they’re “typically possessed by law-abiding citizens for lawful purposes.” If so, then the Second Amendment presumptively protects their ownership. Governments who wish to ban the sale and possession of ARs and magazines would then have the burden of proving that such restrictions have a historical analogue near the time of the founding.

Presumably, items owned by nearly one-third and one-half of all gun owners, respectively–at numbers ranging from tens to hundreds of millions in civilian possession–would satisfy a “common use” test. Home defense and recreational shooting certainly qualify as “lawful purposes” for which such items can be used as well.

The few historical analogues for complete categorical bans on types of arms rely upon the regulation of dangerous and unusual weapons. But courts may find a weapon that is “in common use for lawful purposes” is definitionally impossible to classify as “dangerous and unusual.”

Under such a test, it’s difficult to see how AR-15 and high-capacity magazine bans survive in court.