Prior to the spring of 1967 there were some odd-ball/ad hoc, or “one off” scopes mounted on M14s, as seen in this post re Sgt Greene’s M14. Beginning in March or April 1967, the US troops in Vietnam started getting a more formal system, which likely negated the need to cobble together something like Sgt Greene’s set-up.
Here’s some history of the M84 (2.2x) scope w/ AWC base and G&H scope rail and rings. There was an urgent request in 1966 for a telescope-equipped sniper rifle for use in Southeast Asia (SEA). U.S. Army Weapons Command (USAWECOM or AWC for short) responded by developing a telescope mount for use with the M14 rifle. The adopted system utilized a side-mounted steel scope mount (“AWC Mount”) leftover WWII-era M1C-based Griffin and Howe (G&H) scope bases with 7/8” rings, and the M84 (2.2X) telescope.
This scope was a design finalized back in April 1945 for use on the M1C (Garand) sniper rifle, but WWII ended in the summer of 1945, and M84s were not put into commercial production until the early 1950s during the Korean War era. (The commercial manufactures were Libby-Owens-Ford, and Leupold & Stevens). Notably, I have read production estimates suggesting that “approximately 30k” or “up to 40k” M84 scopes may have been produced during the 1950s.
The M84 scopes were rather outdated by 1966 due to its low magnification compared to other military scopes being used at that time, but they were relatively robust, and readily available in large numbers within the Army’s supply system. So, several hundred M84 scopes, WWII-era G&H scope bases, and the newly designed AWC M14 scope mounts were shipped to Vietnam in 1967.
This optical system was immediately pressed into service, and presumably used until the end of U.S. combat operations in the Vietnam War. They are often seen in vintage pictures on M14 rifles equipped with the M1C/M1D type leather cheek piece pad installed.
Production note: According to Peter Senich’s book, The Long-Range War, Rock Island Arsenal shipped 125 ‘match-prepared’ M14 rifles equipped with the AWC/M84 optic system to Vietnam in March 1967, and an additional 425 loose mounts and 356 M84 scopes were also subsequently sent. So reportedly 550 of the AWC scope mounts were shipped to Vietnam. Rifles equipped with this optical system are sometimes called ‘pre-XM21’ sniper rifles. They were used concurrently with the arrival of the AR TEL 3-9x scopes on XM21 rifles that were first fielded in late 1968, and subsequently standardized in Sept 1969.