Our friends at ‘Loose Rounds’ posted an interesting writeup on sniping that was conducted with the M16A1 during the Vietnam War time period. Check it out at this link : http://looserounds.com/2019/07/11/sniping-with-the-m16a1/
The Colt AR-15 Resource
"A site dedicated to the history of the Colt AR-15 rifles, carbines and associated items"
The Colt AR-15 Resource 