Expanding bullets, also known colloquially as dumdum bullets, are projectiles designed to expand on impact. This causes the bullet to increase in diameter, to combat over-penetration and produce a larger wound, thus dealing more damage to a living target. For this reason, they are used for hunting and by most police departments, but are generally prohibited for use in war. Two typical designs are the hollow-point bullet and the soft-point bullet.
Function and use
Expanding bullets are designed to expand on impact, sometimes as much as twice the diameter. This will slow the bullet down and more of its kinetic energy will be transferred to the target, creating a larger wound channel. For this reason, expanding bullets are often used in hunting because their stopping power increases the chance of a quick kill. There are a number of designs used for hunting different game and for use in weapons with different muzzle velocities. Bullets used for medium and large game need better penetration, which means bullets designed to maintain integrity and for less expansion. The velocities at which the bullets hit affect their expansion and penetration.
Expanding bullets are less likely to pass through the target, and if they do, they will exit at a lower velocity. This reduces the risk of accidental injury to bystanders. For this reason, and to maximize the stopping effect, law enforcement organizations use expanding bullets. Even then, some penetration is needed, e.g., to penetrate a windshield or heavy clothing. Such a bullet would have less possibility of penetrating body armour or heavy equipment worn on the body.
Names
Expanding bullets were given the name Dum-dum, or dumdum, after an early British example produced in the Dum Dum Arsenal, near Calcutta, India by Captain Neville Bertie-Clay. There were several expanding bullets produced by this arsenal for the .303 British cartridge, including soft-point and hollow-point designs. These were not the first expanding bullets, however; hollow-point expanding bullets were commonly used for hunting thin-skinned game in express rifles as early as the mid-1870s. Neither was the .303 the first military round with this trait, the old .577 Snider bullet had a hollow core, leaving wounds known for being particularly nasty. The use of the term "Dum-dum" applied to expanding bullets other than the early .303 designs is considered slang by most ammunition and ballistics sources. Manufacturers have many terms to describe the particular construction of the various types of expanding bullets, though most fall into the category of soft-point or hollow-point designs. The expansion itself is sometimes called mushrooming.
Another early name was General Tweedie's "mushroom bullet", cited in The New York Times in 1892.
History
Early bullets were typically made in the form of spheres of nearly pure lead, which is a very soft metal. These would often flatten upon impact with the target, causing a wound larger than the original diameter of the ball. The adoption of rifling allowed the use of longer, heavier bullets, but these were still typically constructed of soft lead and would often double in diameter upon impact. In this case expansion was a side effect of materials, and there is no evidence that the bullets were designed to expand upon impact.
The earliest examples of bullets specifically designed to expand on impact were those fired by express rifles, which were developed in the mid-19th century. Express rifles used larger powder charges and lighter bullets than typical for the time to achieve very high velocities for black powder cartridges. One method of lightening the bullets used was to provide a deep cavity in the nose of the bullet. These were the first hollow-point bullets, and in addition to developing higher velocities, they also expanded significantly upon impact. These hollow-point bullets worked well on thin-skinned game, but tended to come apart on bigger game, resulting in insufficient penetration. One solution to this was the "cruciform expanding bullet", a solid bullet with a cross-shaped incision in the tip. This split section expanded only to the depth of the incision, making it an early form of controlled expansion bullet.
