A little off subject but not much - the AR-15 is not a military weapon. It was originally designed and sold as a civilian weapon and has never been used by the US Military.
“... the AR-15 is not a military weapon. It was originally designed and sold as a civilian weapon and has never been used by the US Military.”
Definitely not the case.
ArmaLite developed the original arm from designs by Eugene Stoner: they called it the AR-10. It was a select-fire arm in 7.62x51mm NATO and ArmaLite hoped it would compete to become the new US standard issue infantry arm.
AR-10 arrived too late to become a serious contender, and as a developmental item suffered some problems. By then, the selection process was nearing its end and the only rifles with any chances were FN’s prototype FAL (T48 in US Ordnance nomenclature) and the T44, an in-house design no more than a slightly-improved Garand. The latter was selected and became the M14 in 1957.
Stoner left ArmaLite. The firm then learned of the Small-Caliber High Velocity program, by which the Ordnance Corps was seeking rifles chambered in cartridges of roughly 22 cal bore size with much higher muzzle velocities. A team at ArmaLite reworked the AR-10 into a rifle of smaller dimensions firing the 222 Remington round; the cartridge was considered insufficiently speedy by the Ordnance Corps and Remington worked up new cartridges of greater propellant capacity. ArmaLite chambered its downsized rifle for the round that became the 223 Remington and named it the AR-15; some were sent to Southeast Asia with advisory teams - field reports were optimistic.
The US Air Force wanted a lightweight rifle to replace its M2 Carbines, which Army Ordnance was now refusing to support after the adoption of the M14. Colt’s was licensed to make the new purely military select-fire AR-15; ArmaLite had no production facilities at the time. Asserting authority as DoD executive agent for small arms, the Army prevailed upon DoD to suspend USAF’s contract, but various field commands arranged for more production and fielding of what soon became the M16.
Colt’s designed a semi-only version of its military rifle and marketed it as the “AR-15,” starting in the 1960s. Many parts did swap with military arms and still do. The first Colt rifle was officially called the SP-1; both that designation and “AR-15” are stamped on early examples.
ArmaLite licensed AR-10 production to Artillerie Inrichtigen in the Netherlands. They produced some 20,000 rifles and sold them around the world. Field reports from locations from Sudan to the East Indies indicated it was an accurate, serviceable, durable arm.