WASHINGTON - Military-style assault weapons, gangster-style Tommy guns, World War II-era bazookas and even sawed-off shotguns - somewhere in the U.S., there is a legal avenue to get each of those firearms and more.
This is thanks to the maze of gun statutes around the country and the lack of a minimum federal standard to raise the bar for gun control in states with weak laws.
An Associated Press analysis found that there are thousands of laws, rules and regulations at the local, county, state and federal levels. The laws and rules vary by state, and even within states, according to a 2011 compilation of state gun laws by the Bureau of Alcohol, Tobacco, Firearms and Explosives.
These laws and regulations govern who can carry a firearm, what kind of firearm is legal, the size of ammunition magazines and more. In some places, a person can buy as many guns as desired.
This maze of laws undermines gun-control efforts in communities with tougher gun laws - and pushes advocates of tighter controls to seek a federal standard. Gun rights proponents say enforcing all existing laws makes more sense than passing new ones.
"If you regulate something on the local or state level, you are still a victim to guns coming into other localities or states," said Laura Cutilletta, a senior staff attorney at the California-based Law Center to Prevent Gun Violence.
In California, most guns come from Nevada, where there is almost no regulation of firearms, Cutilletta said, and in Arizona, gun owners don't need a permit.
President Barack Obama earlier this month announced a $500 million plan to tighten federal gun laws. The December shooting massacre in Newtown, Conn., that killed 20 children and six adults at an elementary school launched the issue of gun control policy to a national focus not seen in decades.
Obama is urging Congress to pass new laws, some of which would set a minimum standard for the types of firearms and ammunition that are commercially available. Democratic Sens. Patrick Leahy of Vermont and Dianne Feinstein of California introduced new proposals this week to increase penalties for firearms trafficking and impose a new assault weapons ban.
The powerful gun lobby says the problem lies in enforcement of existing laws.
"Which begs the question: Why are we putting more laws on the books if we're not enforcing the laws we already have on the books?" said Andrew Arulanandam, spokesman for the National Rifle Association.
New gun laws will face tough opposition in Congress, particularly from members who rely on the NRA during election campaigns. The NRA contributed more than $700,000 to members of Congress during the 2012 election cycle, according to the Center for Responsive Politics.
Recognizing the opposition in Congress, states already are passing their own new gun laws while officials from some states are promising to ignore any new federal mandates. As the national debate on gun control and Second Amendment rights escalates, the terms being used won't mean the same thing everywhere, due to the thousands of laws, rules and regulations across the country.
"The patchwork of laws in many ways means that the laws are only as effective as the weakest law there is," said Gene Voegtlin of the International Association of Chiefs of Police. "Those that are trying to acquire firearms and may not be able to do that by walking into their local gun shop will try to find a way to do that. This patchwork of laws allows them to seek out the weak links and acquire weapons."
Obama wants to address this, in part, by passing federal gun-trafficking laws that carry heavy penalties. It's difficult to crack down on trafficking because the penalties are too low to serve as a deterrent, and federal prosecutors decline many cases because of a lack of evidence. For instance, in order to charge someone with willfully participating in a business of selling firearms without a license, the ATF needs to prove that the guns were not sold out of the suspect's private collection, the Justice Department inspector general has said.
Obama has also called for a new federal law banning magazines that carry more than 10 rounds of ammunition - a measure that was in effect during the previous assault weapons ban, between 1994 and 2004. High-capacity magazines have been used in recent deadly mass shootings, including those in Newtown, and in the suburban Denver movie theater attack last summer.
But like many terms in the firearm lexicon, a high-capacity ammunition magazine means different things in different places.
In California, considered by many to have some of the strongest gun laws in the country, a large-capacity magazine is one that holds more than 10 rounds. In Illinois there is no state law regarding magazines. Yet, there are laws regarding magazines in Chicago where the threshold is more than 12 rounds. But about 40 miles away in Aurora, Ill., this type of magazine is called a large-capacity ammunition feeding device and means anything more than 15 rounds.
In 44 states, including Arizona, Colorado, Connecticut, Texas and Virginia where these magazines have been used in deadly mass shootings, there are no laws against using them, according to a 2012 analysis by the Law Center to Prevent Gun Violence. If a federal law banned magazines that hold more than 10 rounds, it would become the minimum standard.
The definition of "assault weapon" also varies. There is no federal definition of an assault weapon, and the meaning of the term is inconsistent even within the gun industry. California defines an assault weapon as a "firearm (that) has such a high rate of fire and capacity for fire-power that its function as a legitimate sports or recreational firearm is substantially outweighed by the danger that it can be used to kill and injure human beings." The law specifically lists 60 rifles, 14 pistols and five shotguns. Neighboring states Nevada and Arizona have no assault weapon restrictions.
Federal law does not prohibit the ownership of any weapon, said Ginger Colbrun, an ATF spokeswoman in Washington. In order to buy or own certain firearms, including automatic weapons, machine guns and bazookas, people do have to apply for permission from the federal government. But as long as the application for a restricted firearm is approved, and there is no state law barring ownership of that type of gun, it's legal.
"There is such a variation in the number of laws that regulate the distribution of guns that there is no adequate minimum standard," said Richard Aborn, president of the New York-based Citizens Crime Commission. "The federal government has an obligation to establish at least minimum standards that have to be complied with before a gun can be sold anywhere in America."
WASHINGTON - Even Americans who have never touched a gun are probably familiar with the looks and names of a few - the military M16, the action-movie's Uzi, the historic Colt .45. The terms thrown around in the national debate over gun control can be harder to fathom.
What's a high-capacity magazine? Which guns are "military style"? Why would a person use an assault weapon?
A primer on some key terms in the debate over President Barack Obama's gun-control proposals:
There are all sorts of semi-automatics - they can be pistols, rifles or shotguns - and they're popular sellers. They fire a bullet each time the trigger is pulled, with no need to manually move the next round into the firing chamber. That means they can fire again as fast as a person can release and pull the trigger, so long as the gun's got more ammunition at the ready. Semi-automatic weapons are popular with hunters, sport shooters and gun enthusiasts.
The sale and manufacture of some semi-automatics deemed to be "assault weapons" was banned for a decade. That law expired in 2004.
The shooters used semi-automatic rifles in the Colorado movie theater attack in July that killed 12 people and injured 70 and in the slaying of 20 children and six adults at a Connecticut elementary school in December.
They're on the battlefield and show up in action movies, but fully automatic weapons aren't common among civilians in the United States.
While a semi-automatic can fire one bullet per trigger pull, an automatic keeps firing bullets as long as the trigger is pulled once. Full automatics range from the Prohibition-era machine guns to modern rifles, pistols or shotguns.
Sales of full automatics are restricted by federal law - buyers need a special permit from the Bureau of Alcohol, Tobacco, Firearms and Explosives. That requires an extensive background check and paying a $200 tax. Some states and local governments prohibit private ownership of full automatics.
In 1994, Congress passed and President Bill Clinton signed into law a ban on some semi-automatic rifles and handguns that were deemed "assault weapons." Defining the term was tricky then and remains controversial today.
Under that now-expired law, some new guns were banned by name, including the Uzi, the AK-47 and the Colt AR-15, which is similar to the military's standard issue M16.
The law also covered some other semi-automatic rifles that are used with detachable magazines - devices that hold ammunition and feed the bullets into the firing chamber automatically. Such rifles were banned only if they had two or more additional characteristics listed in the law, such as a folding stock or a pistol grip.
Guns already sold to buyers before the ban were exempt and could be resold. Meanwhile, manufacturers skirted the ban by producing similar guns under new names or making minor design changes, such as removing a bayonet mount.
Obama says he wants Congress to ban what he calls "military-style assault weapons," but he hasn't defined the term, so it's unclear which guns would be covered. He describes his plan as reinstating and strengthening the 1994 assault weapon law.
That 1994 law, however, wouldn't have covered the military-looking Bushmaster .223 rifles used in the Aurora, Colo., and Newtown, Conn., shootings, had it still been in place in 2012. The old law did apply to another aspect of those shootings - high-capacity magazines.
Why would a person use an assault weapon? They are considered by some people to be fun to shoot; they can be used for hunting, depending on the weapon and the size of the animal; and because they resemble military rifles they can appear particularly menacing when used for personal defense or home protection.
Obama wants to reinstate the ban on sales of new high-capacity magazines, defined as those that hold more than 10 rounds of ammunition.
These magazines allow a shooter using a semi-automatic weapon like the Bushmaster .223 to fire more bullets before pausing to reload. Police said Connecticut school attack suspect Adam Lanza had several 30-round magazines with him. In the Colorado theater attack, police have said suspect James Holmes used a 100-round drum magazine.
More than a third of Americans - 36 percent - say someone in their household owns a gun, according to an Associated Press-GfK poll conducted Jan. 10-14.
Millions use guns for hunting, sport and target shooting. Hunting guns include an array of shotguns and rifles of various types and sizes, including semi-automatics and the traditional bolt-action rifles. The prey and a hunter's personal preference determine the weapon and the kind of ammunition used.
Some people keep guns solely for protection. Carrying a concealed handgun is legal in every state but Illinois under certain conditions; for example, the gun owner might need to pass a background check first. Some states require safety classes. Some state and local laws, including in California and New York, make it difficult if not impossible to get a license to carry a concealed weapon. Illinois law bans carrying concealed weapons, but a federal appeals court overturned that law in December. The ruling is likely to be appealed.
Federal laws prevent the government from tracking how many guns are sold every year and who buys them, so there are no definitive statistics.
Roughly 310 million guns were owned or available for sale in the United States in 2009, according to a study by the nonpartisan Congressional Research Service. That's about 114 million handguns, 110 million rifles and 86 million shotguns.
Federal law requires anyone who buys a gun from a licensed dealer to submit to a background check. Convicted criminals and people who have been declared by a judge to be "mentally defective" are among those barred from buying a gun.
The Brady Campaign to Prevent Gun Violence says as many as 40 percent of all gun sales are completed without a background check. That's because sales between private gun owners and sales at gun shows are exempt under federal law.
Only California and Rhode Island require background checks for sales between private sellers and buyers. Colorado, Illinois, New York and Oregon require background checks for all sales at gun shows. Three other states, Connecticut, Maryland and Pennsylvania, require such reviews for handgun sales.
Obama has proposed a federal law requiring universal background checks for every gun sale.
It's the Constitution's Second Amendment that guarantees the right to "keep and bear arms."
The actual text reads: "A well regulated militia being necessary to the security of a free state, the right of the people to keep and bear arms shall not be infringed." What that means has been debated and argued for decades.
The Supreme Court in 2008 ruled that Americans have a right to firearms, regardless of whether they serve in a militia. The justices also have signaled that some gun regulations could survive legal challenges, but they haven't resolved which ones are permissible.