Here’s a little history for you shooters who may be interested. In early Vietnam, we were using the M82 and M 84 scopes. They were 2.5 and 2.2 power scopes. They had a tendency to rust and fail. The mounts were not particularly durable and they would fog up. The longest shot with one of these scopes was 800 m and it took three shots to get the hit.
Second Lieutenant James Leatherwood was working on his scope in 1965 or so at Fort Benning. He was sent to Vietnam with first infantry and was working on his design which ultimately became the ART scope, adjustable ranging and trajectory. It was a breakthrough, they used a 3 x 9 Redfield scope with the specialized 7.62X 51 round, the M118 match round referred to as “camp Perry ammo”
The way it worked was you would frame your enemy target either 18 inches or 36 inches and the ballistic cam would raise or lower the mount which would calculate your distance and compensate for elevation.
They recognized a critical need for an effective sniper system and the LWL, limited warfare lab helped develop the XM 21 that I trained on. It was a match M 14 with a glass bedded stock, headspace minimized, sweet trigger and otherwise developed to very tight tolerances.
In mid 1967 they built 10 XM 21s with the art scope. They were sent to Vietnam and evaluated with very impressive results. 300 m targets, fairly inexperienced shooters and they were getting first round hits.
Camp Bearcat was the first sniper school in October 68. Requirements were for 2020 vision, expert qualification and they preferred competitive shooters. The training was 18 days and there was a 50% failure rate.
The instructors for the original sniper school were members of the “presidents 100“ who were recognized as the top rifle shooters in the United States. Many of them came from camp Perry of course and were automatically qualified for Secret Service duty. The. ART standards were 130 of 160 possible points. The cool thing about the scope was that you could zoom out to scan for enemy and then zoom in to shoot so the scope system acted as its own rangefinder and all you did was calculate your wind. I remember some weird thing where we were taught to drop dead grass and then point at where it landed and divide that angle by half and that was supposed to be your windspeed and direction.
Many guys in combat would zero their system at 600 yards and then glue the settings semi permanently. To calculate their drop, they would shoot for the forehead over 600 m and the crotch under 600 m . By the early 70s when I was trained, the bugs had largely been worked out and the ART System had become a valuable force multiplier in combat.
I don’t know how I remembered a lot of this, sometimes I can’t recall where I parked my car.