The latest reports from the Stockwell Two trial, in which the Metropolitan Police are corporately in the dock for wrongly shooting dead Jean Charles de Menezes in 2005, have it that the plods used "dum dum" bullets.

Even after all this time, the term "dum dum" still carries misty pejorative connotations in the British public mind, so here's the Reg defence desk with a bit of background.

In essence, a hollowpoint slug - as used by the Met on de Menezes - is indeed very close to what's understood by the term "dum dum", though there are some minor differences. Essentially, dumdums/softnose/hollowpoints appeared as an attempt to restore the lost messiness of wounds produced by old-time black gunpowder firearms. The old smoke-poles threw fat, soft, fairly slow lead slugs which blew big holes in people when they hit.

When modern nitro powder came in towards the end of the 19th century, you got a lot more poke behind your bullet; so much so that the soft lead tended to strip away on the rifling grooves inside the barrel, such that the remaining core lost its spin stabilisation and thus its accuracy.

The solution was to coat the lead projectile in tougher metal, which could survive the heat and friction generated by nitro propellant. Such rounds are in use to this day, and their name has been made famous even to people who don't know guns by Stanley Kubrick - it is Full Metal Jacket (FMJ).

FMJ slugs, by their nature, are less prone than a soft-lead musket ball or whatever to smear and spread when they hit something. They're narrower too, and move faster. They will often punch through a human or animal target and emerge on the other side still going at some speed, which is frequently seen as a waste of good kinetic energy.

Some of the first widespread users of jacketed slugs were the British, and as always happens when new kit comes in, military soreheads were soon grousing that FMJs lacked the semi-mythical quality of "stopping power"; that is, they were less likely to knock an enemy down in one than old-school fat lead.

In response, the Dum Dum arsenal near Calcutta - the northwestern Raj being the main combat theatre of the day - tried stripping away some of the harder metal from the tip of jacketed slugs, where it wasn't necessary for the bullet's integrity during firing. This left the soft lead core exposed, so as to spread on impact.

Different methods were tried, both at Dum Dum and later elsewhere, to encourage the bullet to mushroom open on entering a target, so as to blow a big hole like an old time Martini or Brown Bess. These different rounds have different names - softnose, hollow point etc - but they can all fairly be described as being in the general class of expanding bullets, or "dum dums" if you will.

There was a strong backlash against expanding bullets after they came out, with many people suggesting they were in some way abhorrent or evil of themselves, and that no civilised soldier would dream of using them on a human being - certainly not a civilised human being, anyway. This was fairly stupid, as the expanding bullets represented no more than a return to the type of trauma inflicted by the previous generation of weapons.

The stupidity was far from one-sided, however, as the original military objections to high-velocity FMJ rifle slugs were also largely rubbish. High-powered ammo of this type does punch a small, neat entry hole compared to (say) a .45 Martini-Henry bullet or - god help us - a .75 Brown Bess musket ball. It does come out the other side and take a lot of kinetic energy with it.