Dum-dum

Expanding bullets are projectiles designed to expand on impact, increasing in diameter to limit penetration and/or produce a larger diameter wound for faster incapacitation. Therefore, they are used for hunting and by some police departments, but are generally prohibited for use in war. Two typical designs are the hollow-point bullet and the soft-point bullet.

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 shootings. 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.

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. 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.

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