IN A turf war in Birmingham, the two gangs involved used the same gun for their tit-for-tat shootings, renting it in turn from the same third party, says Martin Parker, head of forensics at the National Ballistics Intelligence Service (NABIS). The paucity of guns in Britain is both testament to the success of its gun-control regime and one of the reasons for it.

Tucked discreetly away on a Birmingham back street, NABIS has become a key weapon in the fight against gun crime. In a nearby laboratory, and in hubs in Glasgow, London and Manchester, the staff of around 40 identify firearms using the marks left on the bullets from them, using a database to determine whether they are from known guns. Where the bullet is found but not the gun, they list it as an “inferred weapon”. When a gun is found, they fire it and check the bullets’ markings to see if they match previous shootings.

Ballistics intelligence has improved recently in two ways. First, it is faster. Previously, months could pass before police officers knew if a gun had been used before, says Iain O’Brien, the head of NABIS. Now NABIS can tell them within 24 hours.

Second, the general intelligence is better. When it is sent a gun, NABIS identifies every occasion it has been used, no matter when or where, and tells all relevant forces. In the past, forensic scientists would tell investigators about recent cases but earlier ones might slip through the net. NABIS has thus been able to put together a national picture of trends in the availability, supply and use of firearms.

Gun crime in Britain was low to start with and is falling. NABIS was set up in 2008 when the police and politicians worried that shootings were on the up. Cases such as the murders of Letisha Shakespeare and Charlene Ellis in Birmingham in 2003 fanned fears. That the police can name such individual victims, however, highlights their rarity. London had 99 fewer shootings in 2012-13 than the previous year, a 20% drop, says detective superintendent Gordon Allison of Trident, the Metropolitan Police’s anti-gang unit.

Shootings are rare because guns are scarce. Some criminals steal legally owned shotguns. Some new ones are posted to Britain using fast-parcel services. Others are smuggled through ports. But the risks are higher and the returns lower than for smuggling drugs. Some crooks also reactivate decommissioned guns. Antique firearms are increasingly popular. During the 2011 riots a 19th-century St Etienne revolver was fired. The use of such heirlooms suggests that it is hard to find new weapons. Bullets are in short supply so volatile homemade ones are often deployed.

Shortages also mean criminals use weapons repeatedly, leaving a useful trail of evidence. Some, like the Birmingham gangsters, hire them from others. Clean guns—ones that have not been used before—are both rare and expensive. Other countries, such as Ireland and Spain, use the same database system, allowing NABIS to share information and track guns beyond Britain’s borders. America uses it too, but tracking the guns used in crimes there would be a Sisyphean task: few guns are used repeatedly there because it is so easy to buy new ones. Gun-starved Britons cannot be so cavalier.