When it comes to legal language, armor-piercing bullets get all of the attention. This so-called "cop-killer" ammunition has been banned since 1986 because it can penetrate bulletproof vests. But in reality, many firearms used today have what gun enthusiasts call stopping power, a weapon's ability to render a target immediately harmless. To improve a gun's stopping power, you can do three things: increase the velocity of the bullet as it leaves the muzzle, increase the mass of the bullet being fired or design the bullet so it inflicts more trauma when it hits the flesh of the target. Rifles deliver more stopping power than pistols because they have much higher muzzle velocities. For example, the muzzle velocity of an M16 rifle is almost four times greater than a Colt M1911A1 pistol [source: Dougherty].
That doesn't mean pistols lack stopping power. In fact, most people who carry handguns for self-defense prefer larger-caliber ammunition -- .40 and .45 caliber and 9 and 10 mm -- to increase the odds that an assailant will go down and not get up [source: Kozak]. And what about gunmen bent on killing or wounding as many people as they can? They don't generally come loaded with .22-caliber target-shooting ammunition. Many of the U.S. mass shootings that have gained so much notoriety in the 21st century have included in the arsenal Glock semi-automatic pistols with larger, more powerful rounds:
- Adam Lanza, the shooter at Sandy Hook Elementary School in Connecticut, wielded a 10 mm Glock and a 9 mm Sig Sauer.
- James Holmes, the gunman accused of killing 12 moviegoers in Aurora, Colo., in July 2012, fired a .40-caliber Glock.
- Jared Loughner, the gunman charged with killing six and severely injuring others, including then-U.S. Rep. Gabrielle Giffords, at an Arizona shopping center in January 2011 used a 9 mm Glock.
- And Seung-Hui Cho, who gunned down 32 people in April 2007 on the Virginia Tech campus in Blacksburg, Va., carried a 9 mm Glock in addition to a Walther P22 pistol.
It should also be noted that Jared Loughner armed his Glock with a 30-round magazine. That configuration -- semi-automatic action combined with a high-capacity magazine -- would be considered illegal under the ban proposed by Sen. Feinstein. But the weapon's stopping power is also significant, which is why we include it as a hallmark of assault weapons.
Author's Note: 10 Hallmarks of Assault Weapons – and What They Do
When you read blow-by-blow summaries of the shootings at schools -- Columbine High School and Sandy Hook Elementary School -- it's easy to feel outrage and horror. But when writing this article, I also tried to think of people in my family who own guns -- my brother-in-law, who uses his handguns for target shooting and in competitions, and my nephew, an avid hunter who feeds his family with game he hunts legally. They are both responsible adults and responsible gun owners. It's this tension that makes gun control such a thorny issue.
- Apuzzo, Matt and Pat Eaton-Robb. "Adam Lanza, Newtown Gunman, Had Hundreds of Rounds of Ammunition." Huffington Post. Dec. 16, 2012. (Jan. 30, 2013) http://www.huffingtonpost.com/2012/12/16/adam-lanza-newtown-gunman-rounds-of-ammuniiton_n_2313017.html
- "Assault Weapons Ban of 2013." Senator Dianne Feinstein Site. (Jan. 30, 2013) http://www.feinstein.senate.gov/public/index.cfm/assault-weapons-ban-summary
- Barrett, Paul M. "Glock: America's Gun." BusinessWeek. Jan. 13, 2011. (Jan. 30, 2013) http://www.businessweek.com/magazine/content/11_04/b4212052185280.htm#p1
- Chivers, C.J. "The Gun." Simon & Schuster Paperbacks. 2010.
- Diaz, Tom. "Semiautomatic Assault Weapons: What Are They? What's So Bad About Them?" Violence Policy Center. May 2003. (Jan. 30, 2013) http://www.vpc.org/studies/hosecont.htm
- Dougherty, Martin J. "Small Arms from the Civil War to the Present Day." Fall River Press. 2005.
- Goode, Erica. "Even Defining Assault Rifles Is Complicated." The New York Times. Jan. 16, 2013. (Jan. 31, 2013) http://www.nytimes.com/2013/01/17/us/even-defining-assault-weapons-is-complicated.html?_r=0
- Harrison, Laird. "4 Myths About Assault Weapons." KQED. Dec. 20, 2012. (Jan. 30, 2013) http://blogs.kqed.org/newsfix/2012/12/20/four-myths-about-assault-weapons/
- Hartmann, Margaret. "What Makes a Gun an Assault Weapon?" New York Magazine. Jan. 30, 2013. (Jan. 31, 2013) http://nymag.com/daily/intelligencer/2013/01/what-makes-a-gun-an-assault-weapon.html
- Hoffman, Lisa. "Semiautomatic weapons used in Aurora, Tucson, Virginia Tech, Newtown Connecticut shootings." KJRH News. Dec. 14, 2012. (Jan. 30, 2013) http://www.kjrh.com/dpp/news/semiautomatic-weapons-used-in-aurora-tucson-virginia-tech-newtown-connecticut-shootings
- Kozak, Brad. "Choosing a Handgun, Part VI: Stopping Power." The Truth about Guns. March 12, 2010. (Jan. 30, 2013) http://www.thetruthaboutguns.com/2010/03/brad-kozak/choosing-a-handgun-part-vi-stopping-power/
- Krouse, William J. "Gun Control Legislation." Congressional Research Service. Nov. 14, 2012. (Jan. 30, 2013) http://www.fas.org/sgp/crs/misc/RL32842.pdf
- Lallanilla, Mark. "What Is an Assault Weapon?" LiveScience. Jan. 17, 2013. (Jan. 30, 2013) http://www.livescience.com/26352-definition-assault-weapon.html
- Palmer, Brian. "How Many Times Can You Shoot a Handgun in Seven Minutes?" Slate. Nov. 9, 2009. (Jan. 30, 2013) http://www.slate.com/articles/news_and_politics/explainer/2009/11/how_many_times_can_you_shoot_a_handgun_in_seven_minutes.html
- Peters, Justin. "This Simple, Legal Add-On Lets an AR-15 Rifle Fire 900 Rounds Per Minute." Slate. Jan. 7, 2013. (Jan. 30, 2013) http://www.slate.com/blogs/crime/2013/01/07/slide_fire_this_simple_legal_add_on_lets_an_ar_15_fire_900_rounds_per_minute.html
- Plumer, Brad. "Everything you need to know about the assault weapons ban, in one post." The Washington Post. Dec. 17, 2012. (Jan. 30, 2013) http://www.washingtonpost.com/blogs/wonkblog/wp/2012/12/17/everything-you-need-to-know-about-banning-assault-weapons-in-one-post/
- Regan, Paul, ed. "Weapons: A Visual History of Arms and Armor." DK Publishing. 2010.
- Vance, Lt. J. Paul. "State Police Identify Weapons Used in Sandy Hook Investigation." State of Connecticut, Department of Emergency Services and Public Protection. Jan. 23, 2013. (Jan. 18, 2013) http://www.ct.gov/despp/cwp/view.asp?Q=517284
- Wallace-Wells, Benjamin. "Adam Lanza's Arsenal." New York Magazine. Feb. 3, 2013. (Feb. 5, 2013) http://nymag.com/news/features/gun-control-newtown-2013-2/index2.html
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