The 10-year statutory ban on the manufacture, transfer or possession of "semiautomatic assault weapons" (SAWs) and "large capacity ammunition feeding devices" (LCAFDs) that are capable of holding more than 10 rounds expired on September 13, 2004. The expiration of the SAW-LCAFD ban has been, and will likely remain, controversial. Bills were introduced that would have extended the ban ( S. 2190 , S. 2498 ), made it permanent ( S. 1034 ), or expanded it to include other "military style" firearms ( H.R. 2038 / S. 1431 ). On March 2, 2004, the Senate passed an amendment to S. 1805 , that would have extended the ban for 10 years, but the bill was not passed. A key consideration for Congress is whether violent gun crimes, particularly crimes involving multiple gunshot victims and gunshot wounds per victim, were reduced by the ban. As in 1994, an underlying question for Congress is whether SAWs are more dangerous than other semiautomatic firearms and, if so, should the ban be extended or made permanent, and possibly expanded to include other "military style" firearms. This report focuses on the use and interpretation of firearms trace data produced by the Bureau of Alcohol, Tobacco, Firearms, and Explosives (ATF). Ban supporters have presented trace data to support extending the ban, making it permanent, and perhaps strengthening it. Ban opponents counter that there are serious limitations regarding these trace data. Meanwhile, researchers continue to debate the proper use and interpretation of these data. Please note that this report provides no coverage of legal challenges to the SAW-LCAFD ban. In statute, "SAWs" were defined in two ways. First, certain firearms, or copies or duplicates of those firearms in any caliber, were defined as SAWs by make (in most cases) and model (such as the Colt AR-15, INTRATEC TEC-9, or revolving cylinder shotguns similar to the Street Sweeper). Second, other firearms were defined as SAWs if they included specified features. A rifle met the SAW definition if it was able to accept a detachable magazine and included two or more of the following five features: (1) a folding or telescoping stock; (2) a pistol grip that protruded conspicuously below the action of the firearm; (3) a bayonet mount; (4) a muzzle flash suppressor or threaded barrel capable of accepting such a suppressor; or (5) a grenade launcher. There were similar definitions for pistols and shotguns that were classified as SAWs. SAWs and LCAFDs that were legally possessed prior to the date of enactment were exempted from the ban and remained legally transferrable under applicable federal and state laws. Notwithstanding statutory definitions, there remains a lack of definitive data on SAWs. For example, the precise number of SAWs in civilian circulation is unknown, as is the number of SAWs used in crime. Nonetheless, there are three sources of limited data on SAWs and their possible use by criminals. Those sources include (1) ATF firearm trace data, (2) crime gun recoveries in certain cities, and (3) data on law enforcement officers killed feloniously in the line of duty. There are limited data about SAWs from firearm traces conducted by the ATF, but the proper use and interpretation of the related data remain a matter of debate. Today, as before the 1994 SAW-LCAFD ban, there are significant questions about the consistent and unbiased collection of ATF firearm trace data. Consequently, at a national level, firearm trace data may not be representative of the types of firearms recovered by police and, hence, may not be representative of guns used in crime. Some researchers, however, find firearm trace data to be a useful measurement of crime gun trends—particularly when such data are limited to localities in which the issue of consistent and unbiased data collection have been at least partially addressed through comprehensive crime gun tracing. Other researchers have long stressed that firearm trace data are not representative samples of crime guns. Neither the Federal Bureau of Investigation (FBI)—the principal federal agency charged with the collection of national crime statistics, nor the ATF have endorsed the use of firearm trace data for purposes other than assisting in ongoing criminal investigations. In August 2004, an assessment on the effectiveness of the ban—commissioned by the National Institute of Justice—was released. Based on firearm recoveries in six cities, this report found that firearms with LCAFDs were used in between 14% and 26% of crimes, leading the study's researchers to conclude that in those cities there were indications that any effects that the ban might have had on reducing firearms-related violent crime might have been offset by an increase in use of firearms equipped with LCAFDs. As with firearm trace data, however, there are significant limitations regarding firearm recovery data for these cities. First, while all of these cities made efforts to include all firearm recoveries associated with murders or other serious crimes in their databases, a relatively small percentage of crime guns were recovered by law enforcement. Second, firearm recoveries may be affected by local and regional enforcement strategies that result in significant variation in recoveries from one locality to another. Third, these cities provided the study's researchers with "convenience samples." Fourth, the cities were not selected randomly. These limitations precluded the study's researchers from testing for statistical significance between the SAWs, other semiautomatic firearms equipped with LCAFDs, and all firearms recovered. Data are also available on law enforcement officers killed feloniously with firearms in the line of duty. SAWs and other rifles that use the same calibers of ammunition were used in over half of these cases (65 of112) in the decade, CYs 1993-2002. Proponents of the ban have recompiled FBI data to show that the SAWS and other firearms, which they describe as "military-style" based on their make and model, were used in one-fifth (41 of 211) of such cases from calendar years (CYs) 1998-2001. It should be noted that it is not possible to determine precisely whether all these firearms were SAWs, nor is it known to what extent these firearms contributed to the ability of the criminals to outgun the police by firing multiple shots without reloading. Ban supporters argue that assault weapons should be prohibited, because they were designed for military purposes, are firearms of choice for criminals, and are not suitable for hunting, competitive shooting, or self-defense. They claim that these weapons include the "military features" that increase capacity of fire (detachable magazines) and ease of fire (pistol grips, barrel shrouds, and other features). Thus, they conclude that SAWs are more lethal than other semiautomatic firearms. Furthermore, proponents of the ban underscore that the impetus for the ban was several mass murders committed with SAWs, and that these firearms are disproportionately—given their relatively small numbers compared to other firearms—used in crimes involving multiple shots fired, multiple victims, multiple gunshot wounds per victim, and police officers as victims. They note that, despite several legal challenges, the ban has been upheld as constitutional by federal courts. Opponents of the ban argue that SAWs are not designed for, or used by, military forces, and that large numbers of law-abiding gun owners use SAWs for self-defense, marksmanship, and hunting. They contend that SAWs are functionally no different from other semiautomatic firearms in that they fire only one round per pull of the trigger, and that the statutorily defined SAW features are largely cosmetic and that these banned firearms are no more lethal than other commonly available semiautomatic firearms. They also cite federal, state, and local data sources that suggest that SAWs were used in a fraction (2%) of violent crimes before the ban, and have been used in about the same percentages since the ban. They view the ban as part of a progressive intrusion on the right of citizens to own firearms. Arriving at a definition of an "assault weapon" that is acceptable to all parties has proved difficult. While some would define an "assault weapon" to include any military-style firearm, others maintain that all semiautomatic weapons are equally lethal. They argue that the lethality of the firearms is constant no matter what largely aesthetic features are incorporated into their design. It is noteworthy that, for many years, the term "assault weapon" was a term of art, marketing attraction, and journalistic device. The 1994 legislation created a statutory definition for the term "semiautomatic assault weapon," but the statutory definition expired with the ban. Moreover, firearm designs come in a very wide variety, and it is often difficult to categorize certain types of firearms according to traditional notions as to what constitutes a "machine pistol," "Carbine," "battle rifle," or an "assault weapon." As a result, some still debate the correct use of the term "assault weapon." According to many firearms experts, "assault rifles" were developed during World War II to provide a lighter infantry weapon that could fire more rounds, more rapidly, and more easily. In other words, the design of these firearms included features that allowed for increased capacity and rate of fire, less weight, and less recoil. To increase capacity of fire, detachable, self-feeding magazines (introduced in the late 1880s) were incorporated into these rifles.