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

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.

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.