Any attempt by Congress to enact new restrictions on gun purchases or ownership faces a reality -- America is a country in which many people own guns, weapons which will not simply disappear with the wave of a legislative wand.

Aside from any discussion over the Second Amendment, the reality of firearms currently available in the country is stark and certain.

With hundreds of millions of firearms already in the possession of Americans, limiting access to guns or limiting gun sales would be a major enforcement challenge.

Here’s a look at some basic data on gun manufacture, imports, and ownership, as well as data on crime committed by people using guns.

How many guns do Americans own?

According to the Congressional Research Service, in 2009 there were an estimated 310 million firearms in the United States (not including weapons on military bases), of which 114 million were handguns, 110 million were rifles, and 86 million were shotguns. The current population of the United States, according to the Census, is around 314 million.

A separate calculation by the Government Accountability Office estimated that 118 million handguns were available for sale to, or were possessed by, civilians in the United States in 2010.

It’s impossible to know for certain how many guns are in private hands because there is no central firearms registry. The 1986 McClure-Volkmer Act forbids the federal government from establishing any “system of registration of firearms, firearm owners, or firearms transactions or distribution.” And the 1993 Brady Act prohibits the establishment of any electronic registry of firearms, firearms owners, or firearms transactions.

How many firearms are manufactured in the United States?

According to the annual statistical report from the federal Bureau of Alcohol, Tobacco, Firearms and Explosives, in 2010 more than 5.4 million firearms were manufactured in the United States. In the 20 years from 1990 to 2010, an average of 4 million firearms were made in the United States every year.

How many firearms are imported into the United States annually?

According to the ATF, 3.2 million guns were legally imported into the United States in 2011, up from 1.3 million in 2001.

How many firms in the United States make and sell firearms?

The National Shooting Sports Foundation, the trade association for the firearms industry, has a membership of more than 7,000 manufacturers, distributors, retailers, shooting ranges, and other businesses.

Companies in the United States that make, distribute and sell firearms employ more than 98,000 people, according to the NSSF. In 2012 the firearms and ammunition industry was responsible for as much as $31.8 billion in total economic activity in the country, according to a study done for NSSF.

Revenues for Sturm Ruger, one of the leading U.S. gun manufacturers increased from $146 million in 2004 to $329 million in 2011; another leading U.S. gun maker Smith & Wesson saw its revenues go from $120 million to $412 million in that same period.

How does the number of murders committed with firearms compare to the number of suicides committed with firearms?

According to the National Center for Health Statistics, in 2011 there were 19,766 suicides committed with firearms and 11,101 homicides committed with firearms.

What percentage of murders are committed by people using guns?

According to the FBI Uniform Crime Statistics, in 2011 firearms were used in 68 percent of the nation’s murders, 41 percent of robberies, and 21 percent of aggravated assaults.

How has the rate of firearms-related murder changed in recent years?

In 2011 there were 14,612 murder victims, of which 9,903 were killed by assailants with firearms, according to the FBI Uniform Crime Reports.

The rate of firearms-related murders in 2011 was 3.2 per 100,000 people – a sharp decline from 1993 when the rate of firearms-related murders was 6.6 per 100,000 people.

The number of firearms-related murder victims dropped from more than 17,000 in 1993 to 9,903 in 2011.

How many Americans have permits to carry a concealed weapon?

According to state data compiled by the GAO, there were approximately 8 million active concealed-carry permits in the United States as of the end of 2011.

“Shall issue” states are states in which the law requires authorities to issue a concealed-carry gun permit to an applicant who fulfills the objective statutory criteria if no reason for denial exists. According to the GAO, the number of shall-issue states increased from 29 in 2002 to 39 this year. In addition the number of states that that do not require a permit to carry a concealed gun has increased from one state in 2002 to 4 states in 2012.

How many purchaser background checks have been performed under the 1993 Brady Act and what percentage of applicants has been denied permission to buy a gun?

In 2009, more than 10.7 million background checks were conducted and about 150,000 people were blocked from making the gun purchase they tried to make.

From 1999 to 2009 the largest number of denials – about 900,000, or 56 percent of all denials – was due to a would-be buyer having a felony conviction. In addition, about 15 percent of denials were due to a would-be buyer having a conviction for domestic violence or being under a restraining order. Only about 1.8 percent of denials were due to mental illness.

Under federal law it is a crime to sell or otherwise transfer a firearm to any person who has been “adjudicated as a mental defective or has been committed to any mental institution.” In addition almost all states have similar laws.

What are the limitations on the data on gun ownership, gun usage and crime?

A 2005 data review done by a panel of criminologists, statisticians, and epidemiologists for the National Research Council concluded that there is a lack of reliable data and “in some instances—firearms violence prevention, for example—there are no data at all.”

The NRC report said that “none of the existing data sources, by itself or in combination with others, provides comprehensive, timely, and accurate data needed to answer many important questions pertaining to the role of firearms in violent events.”

The panel reported that “even some of the most basic descriptive questions cannot be answered with existing data.” It cited such unanswered questions as:

• What proportion of suicide or homicide victims were under the care of a mental health professional? What proportion of those victims were intoxicated at the time of death?

• In what proportion of spouse or intimate-partner homicides committed with a gun does the offender take his own life or the lives of the victim’s children or protectors?

• Did the number of people shot with “assault weapons” change after Congress enacted the 1994 ban on certain types of such weapons?