Here's how the polarizing M16 or AR-15 rifle went from a symbol of America's lost war in Vietnam to being owned by about 16 million Americans in 70 years
Reporter Betsy Halstead learns how to fire an M16 automatic rifle during the Vietnam War in 1965.Bettmann/Getty Images
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<li>The M16 or AR-15 rifle is one of the US's most divisive symbols</li>
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