What's the difference between a semi-automatic weapon and a machine gun?

colt, glock semiautomatic gun
An assortment of Colt and Glock semi-automatic handguns on display at the Nations Gunshow in Chantilly, Virginia, 2009. See more pictures of guns.

Mass shootings in a Connecticut school, a Colorado movie theatre and a Tucson supermarket have revived the debate on "assault weapons" and their place in modern society. Trying to flip through the cable news channels without catching a glimpse of the argument -- which usually features one person from each side of the issue talking over the other, building to a crescendo of incomprehensible babble -- is the equivalent of attempting to reach out and touch the moon from your couch.

One problem with the debate is that few people seem to agree on what the term "assault weapon" means. Are we talking about tanks and grenade launchers only? What about the large revolver that Dirty Harry used to lug around? That thing certainly seems like it's capable of "assaulting" someone. To get to the heart of the issue, it's a good idea to first understand the differences between certain types of firearms. Machine guns and semi-automatic weapons, for example.


A machine gun is a military weapon capable of fully automatic fire. That is, the weapon continues to fire until it runs out of ammunition, so long as the trigger is pulled down. In the United States and elsewhere around the world, these weapons are likely to only be found on a battlefield [source: Violence Policy Center].

A semi-automatic weapon, on the other hand, could be described as a civilian version of a military machine gun, one that is less capable of rapid fire. Although the firearm automatically reloads, a shooter must pull the trigger separately in order to fire another round. Semi-automatic weapons are typically pistols, rifles and shotguns, including the AK-47 and AR-15 rifles, the UZI submachine guns, and MAC-10 machine pistols. These firearms are often referred to as "assault weapons," based on their rapid-fire capability. Gun rights advocates have taken issue with the term, however, arguing that it only applies to fully automatic, "spray firing" weapons [source: Violence Policy Center].

There are, generally speaking, two types of machine and semi-automatic guns: recoil-operated and those powered by gas. In the former, the "blowback" or recoil force that occurs when a shot is fired sends the barrel backward rapidly, ejecting the empty bullet shell casing and loading a new bullet into the chamber. A gas-operated gun, meanwhile, harnesses the gas from a fired round to drive a piston in the weapon's barrel, which ejects the spent shell and cocks a fresh one. The automatic load feature in both types of operating system means the user does not need to cock the weapon hammer in order to load a new round [sources: National Institute of Justice].


The History of Machine Guns and Semi-automatic Weapons

army  machine gun
A group of U.S. Army soldiers clear an abandoned building using machine guns. Fully automatic machine guns are seen mainly in the military.
Jacom Stephens/Vetta/Getty Images

Crude versions of the machine gun, including the hand-crank-operated Gatling gun, first came into use during the American Civil War. Invented by Richard J. Gatling in 1862 and an integral part of the U.S. military arsenal until 1911, the Gatling gun used multiple barrels in a cylinder position to fire up to 600 shots per minute. The gun was not fully automatic, however, because it required users to continuously turn the crank in order to keep firing. The first fully automatic weapon was created by Hiram Maxim in 1885; his Maxim machine gun used a recoil system to fire up to 500 rounds per minute [sources: LSU Civil War Center, Spartacus Educational].

It wasn't until World War I, however, when machine guns similar to those seen today came into regular use on the battlefield. As the guns became lighter, including those added to planes, forces on both sides also more regularly used the weapons in place of single-shot bolt action rifles [source: Duffy].


The first widely seen semi-automatic pistol, meanwhile, was created by John M. Browning in 1910 and originally used by U.S. soldiers the following year. Browning and company produced nearly 2 million of its Long Colt pistols during World War II and the .45-caliber weapon was the official sidearm for U.S. Army soldiers for nearly 75 years. In 1914, Browning also introduced the first semi-automatic rifle, a .22-caliber weapon that saw heavy action in World War II [sources: Browning, Johnston, Smithsonian].

With the advance of gun technology came the dawn of gun control. Fully automatic machine gun-type weapons have been tightly regulated since Congress passed the National Firearms Act of 1934, largely in response to the growing prevalence of weapons like the Thompson submachine gun ("Tommy gun"), a machine gun with the cartridge of a pistol. Originally developed for use in World War I, the Tommy gun later became popular among Prohibition-era bootleggers and gangsters before the ban [source: Higginbotham].

From there, the story of gun control in the United States has been a cat-and-mouse game of sorts with gun control activists pushing for laws reflecting ever-developing firearm technology, while gun owners and Second Amendment buffs resist further regulation of their constitutional right to bear arms.


Gun Control

In 1994, U.S. lawmakers passed a federal assault weapons ban, aimed at getting semi-automatic weapons off the streets. The Public Safety and Recreational Firearms Use Protection Act, which expired 10 years later, did little to appease folks on either end of the gun control debate. Nevertheless, politicians, citizens and lobbyists on both sides continue to debate whether the law, or something similar to it, should be revived [source: Plumer].

For those seeking to thwart high-capacity "assault" weapons, the ban was marked by loopholes that allowed manufacturers to skirt the law with a few design changes here and there. For starters, the law did not prohibit all semi-automatic weapons, a move which would have applied to the vast majority of guns on the market. Instead, the act banned 18 specific gun models, including certain types of AR-15s and AK-47s and only those manufactured after 1994 [source: Plumer].


Gun control advocates called the ban toothless, noting that several of the prohibited design features -- bayonet mounts, grenade launchers, silencers and flash suppressors -- don't get to the heart of why these weapons are dangerous: Their ability to fire off several rounds in a short period of time. The law did, nevertheless, limit magazines capable of carrying more than 10 bullets [source: Plumer].

For many gun owners and the well-funded lobbyists at the National Rifle Association (NRA), the ban was an unnecessary invasion on their constitutionally guaranteed right to bear arms. Nor, according to these folks, does a gun ban do much to deter violence. Take away a criminal's pistol and he'll use a knife or a crowbar is one argument. "More guns, less crime" is another. The NRA says that from 1991 to 2012, the murder fell by half while the number of semi-automatic guns rose by 50 million [source: NRA].

As the debate continues, recent gun control efforts have focused on establishing a more robust ban on semi-automatic weapons, as well as a clamping down on highly unregulated gun shows, at which private individuals who are not considered dealers can sell guns without conducting a background check. Meanwhile, local gun control efforts have moved forward in cities and states across the country. Although the U.S. Supreme Court ruled in 2008 that an all-out ban on guns is unconstitutional, very tight restrictions remain in effect in places like New York and Massachusetts [source: Plumer].

We haven't run out of firepower just yet. Check out the links on the next page for more information on machine guns and semi-automatic weapons.


Semi-Automatic Gun FAQ

What's the difference between a semi-automatic weapon and a machine gun?
The difference between these types of gun is that a semi-automatic weapon can be used by civilians whereas a machine gun is only used by military personnel. A machine gun can fire continuously, as long as it’s triggered and doesn’t run out of bullets.
Is an AR-15 semi or fully automatic?
An AR-15 is a civilian version of the M-16 that is used in the armed forces. Since it’s a counterpart of the M-16, the AR-15 is semi-automatic, meaning you need to pull the trigger every time you intend to fire a bullet.
What guns are semi-automatic?
There are many semi-automatic weapons, including MAC-10 pistols, UZI submachine guns, rifles, pistols, shotguns and AR-15 rifles.
Is an AK-47 fully automatic?
AK-47s are available in both semi and fully automatic versions. However, the fully-automatic model is banned in the U.S., so you can only buy a semi-automatic model as a civilian.
How much does a semi-automatic weapon cost?
Semi-automatic weapons are cheaper than fully-automatic. For example, if you buy an new semi-automatic weapon - for example, the popular AR-15 - it can cost as little as $500. However, a fully-automatic weapon can easily cost upwards of $15,000.

Lots More Information

Author's Note: What's the difference between a semi-automatic weapon and a machine gun?

"Leave the gun, take the cannoli," mob strong man Peter Clemenza tells an associate after shooting a traitorous ex-employee in "The Godfather." When it comes to Americans' health and safety, however, it's debatable whether firearms or pastries are doing the most damage. Gorging ourselves at the buffet of excess, our guts are swelling, arteries are clogging and muscles are atrophying, one jelly donut at a time. Meanwhile, the costs associated with obesity-related heart disease, diabetes and cancer continue to balloon. The American Public Health Association projects that "left unchecked, obesity will add nearly $344 billion to the nation's annual health care costs by 2018 and account for more than 21 percent of health care spending." Smart, reasonable gun control is an admirable cause. So is carb control.

Related Articles

  • Browning. "What is the historical timeline for Browning?" (Jan. 21, 2013) http://www.browning.com/customerservice/qna/detail.asp?ID=202
  • Duffy, Michael. "Weapons of War - Machine Guns." Firstworldwar.com. Aug. 22, 2009. (Jan. 21, 2013) http://firstworldwar.com/weaponry/machineguns.htm
  • Higginbothom, David. "Gun Law 101: National Firearms Act of 1934." Guns.com. Jan. 3, 2013. (Jan. 21, 2013) http://www.guns.com/2013/01/03/gun-law-101-national-firearms-act-of-1934/
  • Johnston, John. "Semi-automatic pistol has quite a history." Lampass Dispatch Record. June 7, 2008 (Jan. 24, 2013) http://www.lampasasdispatchrecord.com/news/2008-06-27/Sports/Semi-automatic_pistol_has_quite_a_history.html
  • LSU Civil War Center. "The Gatling Gun." April 6, 2005. (Jan. 21, 2013) http://www.civilwarhome.com/gatlinggun.htm
  • National Institute of Justice. "Firearm Examiner Training." (Jan. 24, 2013) http://www.nij.gov/training/firearms-training/module03/fir_m03_t05_06_e.htm
  • NRA. "NRA Response to President Obama's Gun Control Proposals." Jan. 16, 2013. (Jan. 21, 2013) http://home.nra.org/#
  • Plumer, Brad. "Everything you need to know about the assault weapons ban, in one post." The Washington Post. Dec. 17, 2012. (Jan. 21, 2013) http://www.washingtonpost.com/blogs/wonkblog/wp/2012/12/17/everything-you-need-to-know-about-banning-assault-weapons-in-one-post/
  • Smithsonian National Museum of American History. "Browning Automatic Rifle." (Jan. 21, 2013) http://amhistory.si.edu/militaryhistory/collection/object.asp?ID=652
  • Spartacus Educational. "Hiram Maxim." (Jan. 21, 2013) http://www.spartacus.schoolnet.co.uk/FWWmaxim.htm
  • Violence Policy Center. "Bullet Hoses." (Jan. 21, 2013) http://www.vpc.org/studies/hoseone.htm