Most people in the UK will have never come across a real gun and the terms used, while they are readily recognisable, need some explanation.
Ballistics is the science concerned with the functioning of firearms and the dynamics of projectiles, from bullets through artillery and right up to rockets.
Forensic ballistics experts are able to determine various characteristics which can link bullets and guns with crime scenes. Different guns will leave distinctive marks on any ammunition fired from them.
The science of ballistics can also be used to determine from what angle and distance a gun has been fired, and this can be useful when trying to work out what has happened at a crime scene.
The barrel length of the gun can vary enormously. Generally, the longer it is and the more rifling it has, the more accurate the weapon will be.
Rifling is the name given to the helix-shaped grooves inside the barrel which help to spin the bullet.
Blank ammunition - blanks - describes cartridges which do not contain bullets. When it is fired, a blank still produces a bang and a flash of light, but only hot gases are emitted - so it is therefore unlikely to cause injury except at very close range, when it can be lethal.
Blanks are frequently used in films, TV and theatre productions, and also during military training.
It is a relatively easy matter for a gunsmith or a criminal with the right training and equipment to convert blanks into lethal ammunition.
The bore, or gauge, is the internal diameter of the gun's barrel. One of the most common types of shotgun is the 12-bore but the actual diameter is .729 inches or 18.53mm.
Most modern guns are designed in such a way that they impart spin to the bullet as it travels down the barrel, and this improves accuracy.
But some shotguns - especially those used by game hunters - are smooth bore, which means the barrel is smooth and has not been "rifled". They tend to be less accurate but spread the shot across a wider area in a cone shape, thus increasing the chances of hitting a target. Their range is limited.
Bullets are the projectiles which are fired from the barrel of the gun at high speed - or velocity - when the trigger is pulled.
Bullets are made of metal (usually lead) and are designed with aerodynamics in mind.
Calibre refers to the size of the ammunition needed by a gun. Calibres for handguns range from the smallest - 2mm - to the largest - .500, which is used in the world's most powerful production revolver, the Smith & Wesson Model 500. The most popular calibre has been the 9mm and the .45.
Generally speaking, the larger the calibre the more damage can be done, but a 9mm gun is just as lethal as a larger calibre gun and is very popular among gangsters and professional hit men.
Shotgun cartridges vary from .410 to two-inch calibre, but the most common type is known as a 12-gauge.
Cartridges are the ammunition used by the majority of firearms.
They are usually cylinders or cases made of steel or brass, which contain gunpowder, a primer and a bullet - or shot.
In an automatic or self-loading pistol, the empty cases are automatically expelled from the gun chamber after firing. The cartridges for handguns are much shorter and sleeker than shotgun cartridges.
The chamber is the part of the gun into which the ammunition is placed. The chamber is sited at the back of the barrel.
Depending on the type of gun, the ammunition is either fed into the chamber by means of a revolving mechanism or pushed up from the magazine.
Dum-dum bullets were invented by the British Indian Army in the 1890s at an arsenal in Dum Dum, near Calcutta.
The inventors realised that by drilling a hole in the bullet, it would expand on impact, thus maximising the amount of damage to the unfortunate individual who was targeted.
A more recent adaptation is the hollow-point bullet, which has a pit in the nose of the bullet which helps to maximise damage on impact.
Under international law, dum-dum bullets have been banned from military use but are used by police forces around the world, partly because they decrease the chances of causing collateral damage to innocent passers-by.
The firing-pin is the mechanism which sets off the primer, causing the bullet to be ejected from the barrel in the ensuing explosion.
When the trigger is pulled it releases a hammer which hits the firing-pin.
Machine-guns were invented in the late 19th Century to maximise firepower on the battlefield. Examples included the Gatling and Maxim guns and the Vickers gun, which were popular with the British Army and needed to be mounted on tripods because of their size.
In 1918 the sub-machine gun was first used by the Germans in their spring offensive on the Western Front.
In America a sub-machine gun was invented by a US general, but too late for use in the trenches. It was the eponymous Thompson sub-machine gun, which was light enough to be able to be carried, was quickly nicknamed the "Tommy gun" and became popular with prohibition-era gangsters such as Al Capone.
This Uzi was seized from a Lancashire gun smuggler
Sub-machine gun design has developed greatly. Two of the most popular are the Israeli-designed Uzi and the American Mac-10, the latter nicknamed the "spray and pray" because of the difficulty of aiming it at a particular target.
It is very rare to find machine guns or sub-machine guns on the streets of Britain.
Some guns, such as self-loading pistols, will store ammunition in a magazine, which feeds them automatically into the chamber.
The magazine can be removed when empty and replaced with a fresh one.
Depending on their size and the type of gun, magazines usually contain from six to 15 rounds, but exceptionally can contain up to 25 rounds.
Although the name pistol dates back to the flintlock era, in common usage it refers to self-loading pistols.
The magazine of this pistol is clipped into the butt of the gun
The semi-automatic pistol is equipped with a magazine or clip of ammunition. Each time it is fired the energy from the recoil is used to automatically discharge the empty case and reload the chamber with a fresh cartridge.
Some famous self-loading pistols include the .45 Colt 1911, the 9mm Beretta, the 9mm Glock 17, the 9mm Makarov and the 7.65mm Walther PPK, the last of which was famously the gun of choice of James Bond
Pistols were banned in the UK following the Dunblane massacre.
Each cartridge will contain a percussion primer, which is usually a copper cap filled with a chlorate mixture. When the primer is struck by the firing-pin it will trigger the main charge and this ejects the bullet from the barrel.
Guns manufactured or sold in the UK have to undergo a proof test to confirm they are safe for use.
During this test, a round is fired. The gun is then marked with a proof mark.
There are two proof houses in Britain which are certified to carry out these tests and administer proof marks. One is in London and the other in Birmingham.
When any gun is fired it produces a recoil, or backward motion. The recoil is more noticeable in more powerful guns.
The force of the recoil is absorbed by the person holding the gun but it can affect the effectiveness of aiming which is why police officers are usually trained to hold firearms steady with both hands.
The first successful revolver was patented by Samuel Colt in the 1830s, but the modern revolver has moved on a great deal since the days of the Wild West.
Most revolvers have five or six chambers which allow the person in possession to fire five or six shots before needing to reload.
One of the most powerful guns in the world is the .44 Magnum revolver, which was made famous by Clint Eastwood in the Dirty Harry films of the 1970s.
Revolvers were banned in the UK in the wake of the Dunblane massacre in 1996. Thomas Hamilton was armed with two revolvers and two pistols.
A rimfire cartridge is so-called because instead of the firing-pin striking the primer in the centre, it strikes the rim.
The most popular rimfire calibre is the .22. It is probable that more weapons have been made for this calibre than any other.
They remain popular because they are relatively inexpensive and easy to use.
Police and the media frequently refer to rounds of ammunition. A round is simply a single cartridge for a firearm.
Some weapons, for example machine-guns, fire multiple rounds and the ammunition is supplied in either belts or magazines.
Police sometimes fire Hatton rounds during siege or raid situations. A Hatton round is a special cartridge made of compressed zinc or lead which, when fired, is designed to blow open a door with minimal collateral damage.
Most pistols are fitted with safety-catches, which are designed to prevent them going off accidentally, for example if they are dropped or fall into the hands of a child.
In recent years many gun manufacturers have built into their products integral locking mechanisms, which can only be deactivated by a unique key. These are designed as anti-theft and child-safety devices.
Shotguns use a specific type of cartridge, often called a shell.
Shotgun shells are considerably larger than handgun cartridges
Shot shells usually consist of a metal primer cap at one end and a brightly coloured plastic casing which holds the gunpowder and shot inside.
Shotguns come in many shapes and sizes but tend to be mainly used by farmers and gamekeepers in rural areas to keep control of vermin and pests like foxes, rabbits and rats.
The stock of the shotgun can be used to absorb the recoil
Shotgun owners must have valid licences and are expected to keep their weapons under lock and key when not in use.
In the 1960s and 1970s the sawn-off shotgun became de rigueur among armed robbers, although their use has since declined.
It is illegal to deliberately shorten the barrel of a shotgun.
Possession of pump-action shotguns is more restricted because they are capable of holding more than two cartridges.
Silencers or suppressors are devices which can be attached to all guns, but mainly handguns, to reduce the amount of noise and flash emitted by the weapon.
A silencer is screwed onto the end of this sub-machine gun
Silencers tend to be long metallic cylinders which are screwed onto the end of the barrel. They are designed to muffle sound by manipulating the escaping gas, and this can result in the speed of the bullet being reduced.
Despite the name, they do not make weapons completely silent. Instead the gun will make a small popping noise rather than a loud bang.
Shotguns and rifles are fitted with long handles known as stocks which are designed to be both gripped by the shooter and placed up to and into the shoulder.
The phrase "lock, stock and barrel" refers to different parts of a gun with the lock referring to flintlock firearms, which are now obsolete.
The handle of a handgun is referred to as a butt rather than a stock.