The "prototype" to the M-16 was, indeed, labeled an "AR-15". However, when adopted by the military it was known as the M-16. That original prototype "AR-15" was an automatic just like the M-16.
The semi-auto only AR-15 available to civilians today is not the same prototype that was adopted as the M-16.
When I read your post, it seems like you are equating today's AR-15 to the M-16 (and the original prototype AR-15). Given your USMC background, I'll give you the benefit of doubt and assume it is merely imprecise writing. I am guilty of this at times as well...
M16 rifle, assault rifle developed as the AR-15 by American engineer Eugene Stoner of ArmaLite Inc. in the late 1950s. The rifle received high marks for its light weight, its accuracy, and the volume of fire that it could provide. The AR-15 was developed as a more portable alternative to the
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