ORLANDO, FLORIDA - The weapon used in a deadly shooting spree at a Florida high school was an AR-15-style semi-automatic rifle, according to media reports.
The AR-15 is a lightweight, 5.56×45mm, magazine-fed, gas-operated semi-automatic rifle and is a semi-automatic version of the United States military M-16 rifle.
The gun is among the must-have weapons for American enthusiasts and figures heavily in popular culture, with the hashtag #ar15 used 1.7 million times on Instagram, with more users uploading images featuring the weapon by the minute.
The weapon, or variants of it, have been used in several mass shootings before the latest incident, including incidents in Aurora, Colorado; Newtown, Connecticut; San Bernardino,California; Sutherland Springs, Texas; and Las Vegas, in which a total of 137 people were killed, reported NBC News.
Consequently, it is as much an object of fascination, as repulsion, and an exceptionally polarising product of modern American industry. It is the country's most popular rifle, with one out of every five firearms purchased in the US an AR-style rifle, according to a National Shooting Sports Federation (NSSF) estimate.
Americans own 15 million AR-15s, which range in price from about US$500 (S$656.43) to more than US$2,000.
The AR-15 was developed in the late 1950s as a civilian weapon by a California start-up called ArmaLite, which is were AR comes from. The gun gained mainstream attention after Colt bought the patent and developed an automatic fire version for troops in Vietnam, the M-16.
The civilian model wasn't mass produced until the 1980s, after the original patent expired. Subsequently, a variety of companies began making them, transforming a specific brand into a more generic offering that spawned a mini-industry.
One of the visceral reasons for the weapon's appeal is the speed at which projectiles leave the weapons, delivering a more devastating blow to bones and organs. What's more, projectiles are also more likely to break apart upon impact, inflicting more damage.
The backlash against the rifles in the US peaked in 1994, when President Bill Clinton signed a ban on the sale of many semi-automatic rifles deemed "assault weapons", including some versions of the AR-15. Manufacturers continued to make variants that did not breach the new law, which expired in 2004.
Subsequently, there was a surge in AR-15 sales: in 2004, 107,000 AR-15s were made. In 2015, the number was 1.2 million.
It is seen by many in the US as the pinnacle of firearms engineering - ergonomic, accurate, reliable - according to NBC News.