The name 'dum-dum' came from a factory location in India where the flat-nosed bullets were first designed. The modern copper jacketed bullet with an exposed lead tip is specifically designed to expand nearly completely. It will virtually turnitself inside-out resulting in a massive wound chanel that kills quickly and humanely in game animals. There is no convention about the use of such buillets in warfare. The purpose of using full metal jacket bullets in warfare is to provide the maximun reliability in the self-loading type of weapons used since WW2. The soft, exposed lead tip sometimes catches on the edge of the breech causing a jam which must be cleared by hand (under fire in the battle scene). It really is that simple.
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from the article: Norway massacre suspect warns of two more terrorist cells