Met used 'dum-dum' ammo on de Menezes
Which would have been fine, if he was a bomber
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.
However, the exit wounds caused by high-velocity FMJ rifle bullets often look more like something done with a spade than with a 5mm to 8mm projectile*. During the Spanish-American fighting on Cuba in 1898, one of the first occasions where large numbers of Western soldiers got hit by such bullets, the horrible nature of the wounds convinced many that the evil Spaniards were using some kind of illegal ammo. In fact, of course, they were shooting "civilised", "gentlemanly" FMJ.
Wound ballistics, then as now, was a hotly disputed subject, and the public debate remained muddled. In 1899 most of the European powers signed up to a convention on the Laws of War during the Hague conference, in which they agreed, when in wars against each other, "to abstain from the use of bullets which expand or flatten easily in the human body, such as bullets with a hard envelope which does not entirely cover the core".
As a result, it is usually seen as a war crime for soldiers to use expanding bullets on other recognised soldiers, though they are perfectly OK if fired at troops of non-signatory powers, or if fired at civilian criminals, terrorists etc. Grenades, napalm, fuel-air bunker-busters, massed artillery, roadside explosive penetrators, bayonets, bows and arrows - they're all fine, even though they rip up a human body far more gruesomely than an expanding slug. In this respect at least, the Laws of War don't make a huge amount of sense - even more so since civilised soldiers started wearing body armour, which expanding bullets can't cope with.
Prior to the de Menezes shooting, the Met had instituted a shoot to kill (or, as they hopefully put it, 'shoot to stop') policy to deal with suicide bombers.
This clearly presented them with difficulties, because there isn't any good way to deal with a suicide bomber on public transport or in any other crowded place. Warning him is likely to cause an explosion. So is the use of a Taser electroshock weapon, though astonishingly foolish/brave regional coppers have been known to take this route with people they believed to be carrying bombs. Standard deadly-force methods - shooting into the body - may trigger an explosive vest, so that's out too.
Thus, the rule is to shoot a suicide bomber in the head and keep shooting until you're sure he won't trigger a bomb. To be honest, it probably won't make any odds to him whether you use FMJ or hollowpoint; but on balance the expanding round is a better choice. It is a tad more sure to take the bomber out of play at once, and it's somewhat less likely to pass through him and hit someone else. Shooting at the head, you don't need to worry about body armour or other obstructions, which are a problem for hollowpoints otherwise. ®
*A note on calibre notation: .45, .303 etc are decimals of an inch, measuring bullet diameter. When using metric, it's normal practice to say so by adding "mm" afterwards. I'm skipping the Reg units for this one because it's complicated enough already. Translate into Bulgarian funbags, weasels' wedding tackle etc at your discretion.