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Large capacity magazines are often used in mass shootings because they allow a shooter to keep firing for longer periods of time, increasing casualties and reducing victims’ ability to escape or intervene.

Large capacity ammunition magazines are a common thread in many high-profile mass shootings in the United States. Because shooters with such magazines can fire at large numbers of people without taking the time to reload, those in the line of fire do not have a chance to escape, law enforcement does not have the chance to intervene, and the number of lives shattered by acts of gun violence increases dramatically.


Although the statutory definitions vary, magazines with a capacity of more than 10 rounds of ammunition are generally considered “large capacity” magazines.

While large capacity magazines are typically associated with semi-automatic assault weapons or machine guns, such devices can be used with any semi-automatic firearm that accepts a detachable magazine, including handguns.

Large capacity magazines (LCMs) have been used to perpetrate devastation on a massive scale in many high-profile mass shootings. In fact, large capacity magazines have been used in all ten of the deadliest mass shootings in the last decade. Large capacity magazines significantly increase a shooter’s ability to injure and kill large numbers of people quickly because they enable the individual to fire repeatedly without needing to reload.

The more rounds a shooter can fire consecutively, the more gunshot wounds they can inflict during an attack.

  • Mass shootings that involve large capacity magazines result in twice as many fatalities compared to mass shootings that do not involve high capacity magazines.1
  • Using an assault weapon and a drum magazine that held 100 rounds, the assailant in the 2019 Dayton, Ohio mass shooting, was able to fire at least 41 rounds of ammunition in less than 30 seconds, killing nine people and wounding 26 others.2
  • The shooter in the 2017 Las Vegas massacre was able to fire 100 rounds in just 10 seconds—without having to pause and reload—because he used a large capacity magazine, bump stock, and an assault rifle in his attack which killed 50 and injured hundreds.3

The time a shooter takes to reload his weapon can be critical in enabling victims to escape and law enforcement or others to intervene. When shooters have high capacity magazines, more bullets can be fired before this crucial time period for escape or other intervention.

  • The 2011 mass shooting in Tucson, AZ, where six people were killed and 13 others were wounded, including US Representative Gabrielle Giffords, was interrupted when the gunman stopped to reload his weapon and was tackled by a bystander.4
  • Similarly, during the 2018 shooting at Marjory Stoneman Douglas High School, students were able to escape down a stairwell while the shooter paused to reload his weapon.5

In addition to their role in mass shootings, firearms equipped with large capacity magazines significantly contribute to crime across the country. Alarmingly, data suggests that the use of firearms with large capacity magazines in crime has substantially increased since the expiration of the federal assault weapons and large capacity magazine ban in 2004.

  • Firearms equipped with high-capacity magazines are estimated to account for 22 to 36% of crime guns in most places.6
  • Estimates also suggest that nearly 40% of crime guns used in serious violent crimes, including murders of law enforcement officers, are equipped with high-capacity magazines.7
  • The share of recovered crime guns equipped with large capacity magazines increased by between 49 and 112% in several major cities—and an estimated 33% nationally—after the 1994 federal ban on assault weapons and large capacity magazines expired.8

A growing body of research shows that banning high-capacity magazines can help to prevent gun violence. In particular, studies have found that the federal ban on large capacity magazines helped to prevent violence and the use of high-capacity magazines in crime during the 10 years in which it was in effect.

  • During the 10-year period the federal assault weapons and large capacity magazine ban was in effect, mass shooting fatalities were 70% less likely to occur compared to the periods before and after the ban.9
  • While the federal assault weapons and large capacity ammunition ban was in effect, the number of high-fatality mass shootings fell by 37%, and the number of people dying in such shootings fell by 43%. When the ban lapsed in 2004, there was a 183% increase in high-fatality mass shootings and a 239% increase in deaths from such shootings.10

Polling consistently shows that a majority of Americans—nearly 70%—support laws a ban on large capacity magazines.11

Summary of Federal Law

The Former Federal Ban

In 1994, Congress adopted the Violent Crime Control and Law Enforcement Act, making it unlawful to transfer or possess a “large capacity ammunition feeding device” not lawfully possessed on or before the law’s enactment.12 The law also banned the manufacture, transfer, and possession of semi-automatic assault weapons. See our summary on Assault Weapons for more information. The law was adopted with a sunset clause, however, and expired in 2004, despite overwhelming public support for its renewal. Thus, large capacity ammunition magazines and assault weapons that were formerly banned under the federal law are now legal unless banned by state or local law.

The 1994 Act defined “large capacity ammunition feeding device” as “a magazine, belt, drum, feed strip, or similar device…that has a capacity of, or that can be readily restored or converted to accept, more than 10 rounds of ammunition.”13 The ban contained a loophole, however, allowing for the continued transfer, and possession of large capacity ammunition magazines manufactured or possessed on or before enactment of the law.

Manufacturers took advantage of this loophole in the months leading up to the ban by boosting production of the magazines. As a result, they continued to be readily available—and legal—nationwide even during the time the 1994 Act was in effect, except where specifically banned by state or local law. Additionally, because most magazines do not have any identifying marks to indicate when they were manufactured, it was difficult to distinguish those made before or after the ban.14


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Effectiveness of the Ban

Despite these limitations, evidence indicates that the federal ban worked to reduce the use of large capacity magazines in crime. A Washington Post study analyzed data kept by the Virginia State Police and found a clear decline in the percentage of crime guns that were equipped with large capacity ammunition magazines after the federal ban was enacted.15 The percentage reached a low of 10% in 2004 and then steadily climbed after Congress allowed the ban to expire; by 2010, the percentage was close to 22%.16

Similarly, since the end of the federal ban, the Los Angeles Police Department has recovered significantly greater numbers of large capacity ammunition magazines, from 38 in 2003 to anywhere from 151 to 940 each year between 2004 and 2010.17

Bans on large capacity ammunition magazines—whether they contain grandfather provisions or not–do not present a problem under The Takings Clause of the Fifth Amendment.

Summary of State Law

Nine states and the District of Columbia have enacted laws banning large capacity ammunition magazines: California, Colorado, Connecticut, Hawaii, Maryland, Massachusetts, New Jersey, New York, and Vermont. All of these jurisdictions except Colorado and Vermont also ban assault weapons.

State Large Capacity Magazine Regulations
StateFor Use w/ Which Firearms Legal Magazine Capacity Limit Prohibited Acts for LCAMs
Treatment of Pre-Owned LCAMs
California18 All Firearms 10 rounds Manufacture, importation, keeping for sale, offering and exposing for sale, giving,  lending, and possession
Not allowed by a law that has not yet gone into effect.19
Colorado20 All Firearms 15 rounds Sale, transfer, and possession
Allowed (“grandfathered”)
Connecticut21 All Firearms 10 rounds Distribution, importation, keeping for sale, offering and exposing for sale, purchase, and possession
Allowed but must be registered.
D.C.22 All Firearms 10 rounds Possession, sale and other transfer
Not allowed
Hawaii23 10 rounds Manufacture, possession, sale, barter, trade, gift, transfer, and acquisition
Not allowed
Maryland24 All Firearms 10 rounds Manufacture, sale, offering for sale, purchase, receipt, and transfer
Allowed (like all LCAMs. There is no ban on possession.)
Massachusetts25 All Firearms 10 rounds Sale, offering for sale, transfer, and possession
Allowed (“grandfathered”)
New Jersey26 All Firearms 10 rounds Manufacture, transportation, shipment, sale, disposal, and possession
Not allowed (Certain firearms with magazines capable of holding 11-15 rounds may be registered until July 13, 2019)
New York27 All Firearms 10 rounds Manufacture, transportation, disposal, and possession
Not allowed
Vermont28 All Firearms 10 rounds for Long Guns; 15 rounds for handguns Manufacture, sale, offering for sale, purchase, receipt, transfer, and possession
Allowed (“grandfathered”)

Categories of Large Capacity Magazine Bans

For citations to these laws, please see the chart above.

States that Ban Large Capacity Magazines for Use with Any Firearm

Eight states (California, Colorado, Connecticut, Maryland, Massachusetts, New Jersey, New York, and Vermont) and the District of Columbia all ban large capacity ammunition magazines for use with any firearm.

State that Bans Large Capacity Magazines for Use with Handguns Only

Hawaii prohibits the manufacture, transfer, and possession of large capacity magazines designed for or capable of use with a handgun.

Definition of Large Capacity Magazine

State laws vary as to how the term “large capacity magazine” is defined: California, Connecticut, Hawaii, Maryland, Massachusetts, New Jersey, New York, and the District of Columbia define a large capacity magazine as a magazine that is capable of holding more than 10 rounds.29 Colorado defines a large capacity magazine as a magazine capable of holding more than 15 rounds. Vermont restricts large capacity magazines that hold more than 10 rounds for use in a long gun, or more than 15 rounds for use in a handgun.

Prohibited Activities

California, Hawaii, New Jersey, and New York have the most comprehensive prohibitions, banning possession, manufacture, and transfer (including sale) of large capacity magazines. New Jersey allows possession of large capacity magazines by a person who has registered a grandfathered assault weapon and uses the magazine in connection with competitive shooting matches sanctioned by the Director of Civilian Marksmanship of the US Department of the Army.30

Other states ban various combinations of activities related to large capacity magazines. For instance, Colorado, Massachusetts, and the District of Columbia ban possession and transfer; Maryland bans manufacture and transfer; and Connecticut bans distribution, importation, purchase, transfer, and possession.

Magazines Owned at the Time of the Ban

State laws that ban the possession of large capacity ammunition magazines vary in their approach to large capacity magazines already in the possession of private individuals at the time a ban was adopted.

States that Do Not Grandfather Pre-Ban Magazines

California, the District of Columbia, Hawaii,31 New Jersey, and New York generally do not allow continued possession of large capacity magazines that were obtained before these states enacted bans on those magazines. As a result, these jurisdictions effectively required any large capacity magazine owned at the time the ban was enacted to be converted to a more limited capacity magazine, destroyed, or transferred to a dealer, law enforcement, or out of state. New York extends a 30-day grace period to any individual in possession of such a magazine manufactured before September 13, 1994, who is unaware that their magazine is illegal. This individual is not required to dispose of the magazine until he or she is notified by law enforcement or county licensing officials that possession is unlawful. Once they receive notice, they have 30 days to surrender or “lawfully dispose” of illegal magazines.

States that Grandfather Pre-Ban Magazines

The Connecticut ban does not apply to large capacity magazines that were lawfully possessed before January 1, 2014, but lawful owners of such magazines must register them with the State Department of Emergency Services and Public Protection within a specified period.

Colorado, Massachusetts, and Vermont all grandfathered possession of large capacity magazines that were owned prior to the effective date of a ban.32

Maryland does not prohibit possession of large capacity magazines, although manufacture and transfer are banned. As a result, individuals who possessed such magazines before these states’ bans may continue to possess them.

States that Require Identification Markings for Magazines Manufactured after the Law

As noted above, enforcement of laws grandfathering pre-ban magazines is difficult because most magazines do not contain any markings to identify those that were manufactured before or after the effective date of the ban. As a result, the Colorado law requires manufactures to include a permanent stamp or marking on all large capacity magazine produced after July 1, 2013. These markings must indicate that the magazine was manufactured after the date the ban went into effect and must be conspicuously engraved or cast on the outer surface of the magazine.

Bans on “Conversion” or “Repair” Kits

In 2013, California explicitly banned the use of “conversion” or “repair” kits that allow the purchaser to construct home-made large capacity ammunition magazines from spare parts.


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Selected Local Law

See the description in our summary on Assault Weapons of the Blair-Holt Assault Weapons Ban in Cook County, Illinois. This law includes a ban on large capacity ammunition magazines.

Key Legislative Elements

The features listed below are intended to provide a framework from which policy options may be considered. A jurisdiction considering new legislation should consult with counsel.

  • Definition of “large capacity ammunition magazine” includes magazines capable of holding more than 10 rounds (Hawaii, California, Connecticut, Maryland, Massachusetts, New York, District of Columbia).
  • Ban applies to large capacity ammunition magazines for use with all firearms (California, Colorado, Connecticut, Maryland, Massachusetts, New Jersey, New York, Vermont, and District of Columbia).
  • Prohibited activities include possession, sale, purchase, transfer, loan, pledge, transportation, distribution, importation, and manufacture of large capacity ammunition magazines (California, Hawaii, New Jersey, and New York are the most comprehensive, banning manufacture, transfer, and possession).
  • No allowance for pre-ban magazines (California, District of Columbia, Hawaii, New Jersey, New York); alternatively, if pre-ban magazines are grandfathered, the owner must register them before a specified date (Connecticut).
  • If the manufacturing of large capacity magazines is permitted, all magazines manufactured after the adoption of the ban must be identified by distinct and legible markings (Colorado).
  • “Conversion” or “repair” kits that can be used to build large capacity ammunition magazines from spare parts are prohibited (California).

  1. “Mass Shootings in the United States: 2009–2017,” Everytown for Gun Safety, December 2018,[]
  2. Holly Yan, Chuck Johnston, and Polo Sandoval, “The Dayton Gunman Killed 9 People by Firing 41 Shots in 30 Seconds. A High-Capacity Rifle Helped Enable That Speed,” CNN, August 5, 2019,[]
  3. Martha Bellisle, “High-Capacity Magazines Get New Scrutiny as Congress Returns,” ABC News, September 2, 2019,[]
  4. Griff Witte, “As Mass Shootings Rise, Experts Say High-Capacity Magazines Should be the Focus,” The Washington Post, August 18, 2019,[]
  5. Initial Report of the Marjory Stoneman Douglas High School Public Safety Commission, January 2, 2019,[]
  6. Christopher S. Koper et al., “Criminal Use of Assault Weapons and High–capacity Semiautomatic Firearms: an Updated Examination of Local and National Sources,” Journal of Urban Health 95, no. 3 (2018): 313–321.[]
  7. Id.[]
  8. ; See also, David S. Fallis and James V. Grimaldi, “VA Data Show a Drop in Criminal Firepower During Assault Gun Ban,” The Washington Post, January 23, 2011,[]
  9. Charles DiMaggio et al., “Changes in US Mass Shooting Deaths Associated with the 1994–2004 Federal Assault Weapons Ban: Analysis of Open–source Data,” Journal of Trauma and Acute Care Surgery 86, no. 1 (2019): 11–19.[]
  10. In this analysis, researchers defined high-fatality mass shootings as those in which six or more individuals were killed. Louis Klarevas, Rampage Nation: Securing America from Mass Shootings (Amherst, New York: Prometheus Books, 2016). See also, Christopher Ingraham, “It’s Time to Bring Back the Assault Weapons Ban, Gun Violence Experts Say,” The Washington Post, February 15, 2018,[]
  11. “Gun Policy Remains Divisive, But Several Proposals Still Draw Bipartisan Support,” Pew Research Center, October 18, 2018,[]
  12. 18 U.S.C. § 922(w)(1), (2). All references to sections of the Violent Crime Control and Law Enforcement Act of 1994, codified at 18 U.S.C. § 921 et seq., are to the sections as they appeared on September 12, 2004.[]
  13. 18 U.S.C. § 921(a)(31)(A). However, “attached tubular device[s] designed to accept, and capable of operating only with, .22 caliber rimfire ammunition” were exempted from the definition. 18 U.S.C. § 921(a)(31)(B).[]
  14. Importation of Ammunition Feeding Devices with a Capacity of More Than 10 Rounds, 61 Fed. Reg. 39, 320 (July 29, 1996) (amending 27 C.F.R. § 178.119).[]
  15. About the Project: The Hidden Life of Guns, Wash. Post, Jan. 22, 2011, at; David S. Fallis & James V. Grimaldi, Virginia Data Show Drop in Criminal Firepower During Assault Gun Ban, Wash. Post, Jan. 23, 2011, at[]
  16. Id.[]
  17. Press Release, Citizens Crime Commission of New York City, NYC & LA City Councils Introduce Rezo for Federal Ban on Large Capacity Ammunition Magazines 2 (Mar. 2, 2011), at[]
  18. Cal. Penal Code § 16350, 16740, 16890, 32310-32450.[]
  19. In 2016, California voters approved a ballot initiative, Proposition 63, which prohibited the possession of pre-owned large-capacity ammunition magazines and was slated to go into effect on July 1, 2017. However, that effective date was delayed after a lawsuit challenging the new LCAM restrictions was filed and a district court entered a preliminary injunction blocking the new law from going into an effect until a final ruling is issued. See Duncan v. Becerra, 265 F. Supp. 3d 1106 (S.D. Cal. 2017), aff’d, No. 17-56081, 2018 U.S. App. LEXIS 19690 (9th Cir. Jul. 17, 2018) (unpublished).[]
  20. Colo. Rev. Stat. §§ 18-12-301, 18-12-303.[]
  21. Conn. Gen. Stat. §§ 53-202w, 53-202q.[]
  22. D.C. Code Ann. § 7-2506.01(b).[]
  23. Haw. Rev. Stat. Ann. § 1348(c).[]
  24. Md. Code Ann., Crim. Law § 4-305.[]
  25. Mass. Gen. Laws ch. 140, §§ 121, 131M.[]
  26. N.J. Stat. Ann. §§ 2C:39-1(y), 2C:39-3(j), 2C:39-9(h).[]
  27. N.Y. Penal Law §§ 265.00(23), 265.02(8), 265.10, 265.11, 265.20(7-f), 265.36-265.37.[]
  28. Vt. Stat. Ann. tit. 13, § 4021 (enacted by 2017 VT S 55, Sec. 8.[]
  29. A law New York adopted in 2013 would also prohibit the manufacture or sale of any magazine that can hold more than seven rounds, and the possession of any magazine that can hold more than seven rounds if it was obtained after January 15, 2013. However, this law has been suspended and will not go into effect without further legislative action. See 2013 N.Y. ALS 1 § 58, as amended by 2013 N.Y. ALS 57 Part FF § 4. As enacted, the law prohibits the possession of any magazine that is actually holding more than seven rounds, except at a shooting range. In December 2013, however, a federal district court struck down this provision as violating the Second Amendment, while upholding several other provisions of the state’s regulation of assault weapons and large capacity magazines. N.Y. State Rifle & Pistol Ass’n v. Cuomo, 2013 US Dist. LEXIS 182307 (W.D.N.Y. Dec. 31, 2013).[]
  30. Additional information on New Jersey’s assault weapon ban is contained in our summary on Assault Weapons.[]
  31. When Hawaii enacted its law in 1992, it allowed individuals in possession of magazines that could accept 20 or fewer rounds to keep them for the following two years. This grandfathering provision expired in July 1, 1994, so individuals in possession of magazines that could accept more than 10 rounds were required to dispose of them before that date.[]
  32. Colorado’s law does not apply to magazines that were lawfully possessed before July 1, 2014;  Massachusetts’s exempts magazines that were lawfully possessed on September 13, 1994 (the date the federal ban took effect), and Vermont’s law does not apply to magazines that were lawfully possessed before April 11, 2018).[]