If you plan to introduce firearms in your mystery, you want to aim for accuracy. Readers and editors who may forgive slight characterization or a contrived plot will positively bristle if your hero thumbs off a revolver's safety.
The information which follows is USA-centric and I apologize in advance to writers from elsewhere in the world. I will also not address gun laws since they differ so much between states.
The Basic Handgun. There are three handgun types: single-shot, revolver, and semiautomatic pistol.
Single-shot handguns such as the Derringer are small, easily concealable guns for those times when surprise counts for more than the ability to spray the countryside. (Some single-shot handguns are actually multiple-shot.)
The revolver is named for the rotating cylinder which houses the cartridges to be fired. The shooter removes the empty cartridges before reloading. Revolvers do not have safeties. They also can not be silenced by attaching a suppressor to the barrel since the sound of the shot comes from the cylinder.
The semiautomatic pistol is loaded from a single magazine which contains the cartridges (up to fourteen in some models). The empty shells are ejected as the gun fires. Many law enforcement agencies are changing from the revolver to the semiautomatic pistol for the higher cartridge capacity and faster rate of fire.
The Basic Long Gun. There are two long gun types: rifles and shotguns.
The rifle, with a longer barrel than the handgun, is used for precise, distance shots. Rifles can be bolt-action or semiautomatic. Because bullets fly in a trajectory, the range to a target affects how much a shooter must correct line-of-sight aim to counter the effects of gravity.
Instead of bullets, a shotgun fires a number of pellets, which disperse once they leave the muzzle. Shotguns are thus most effective at short range. The barrel can be sawed-off for easier concealment.
The Basic Machine Gun. A machine gun is fully automatic gun which can fire rapidly and continuously so long as the trigger is pulled. Examples include the Israeli UZI and the American MAC-10.
According to the "Annual Firearms Manufacturing and Export Report" produced by the Bureau of Alcohol, Tobacco and Firearms (AFT), following is what was added to the mix of available weapons by American companies in 2000:
Some percent of these weapons are not available to the general public. On the other hand, foreign manufacturers not included in these numbers account for a fifth of the total US weapons pool, according to the US Department of Justice.
According to the "1999 Crime Gun Trace Reports" produced by the AFT, firearm type by possessor played out as follows.
The report summarized crime guns traces in 32 of the 79 US cities with populations of 250,000 or more. I imagine the numbers would differ in suburban and rural areas.
According to the National Crime Victim Survey (NCVS) for 1993, only 25% of the rape, sexual assault, robbery, and aggravated assault cases involved a gun.
According to the FBI's "Supplemental Homicide Reports" for that same year, 57% of all murders were committed with handguns, 3% with rifles, 5% with shotguns, and 5% with unknown guns. That leaves 30% of the murders being committed with something other than a firearm.
It's worth noting, however, that according to the Bureau of Justice Statistics, "No national collection of data contains detailed information about all of the guns used in crimes." ("Guns Used in Crime," July 1995.)
Firearms Identification: If a bullet can be recovered in good enough shape, unique markings can be matched to another bullet fired from the same gun. (The same is not true of shotgun pellets.) While the identification is as solid as fingerprints, the gun must first be recovered to perform the test.
Guns and the Senses: The sight and sound of gunfire is no stranger to anyone who watches television or goes to the movies. If you want to make your use of guns stand out from the crowd, don't forget touch, taste, and smell.
Most guns are metal and wood and rubber. They weigh anywhere from half a pound to almost ten. When a shot is fired, there is a kickback, the strength depending on the specific gun and its muzzle velocity.
Gunpowder blown into the air has a taste and a smell. You may wish to visit a firing range so you can experience and describe the particulars yourself.
Movie Magic to Avoid: There are three accepted movie-isms that shouldn't find their way into your fiction:
Additionally, warning shots are banned by most law enforcement agencies for any number of good reasons.
Before you choose a weapon, pick up one of the many books or magazines devoted to guns. Research basic types and specific models for accuracy. Many firearm manufacturers have an Internet site which will give you further specifications and links to available accessories. Once you have determined the setting of the story, check that locations's local and state police departments for their crime and gun statistics.
While the bulk of gun information available on the Internet is geared towards the pro/con arguments for and against gun control and the right to bear arms, even this can provide useful flavoring for characterization.
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