On a muggy February afternoon in 1969, a US Army landing craft meandered down the Mekong River on a routine patrol mission. The boat was about a thousand yards away from the shore, safe from enemy AK fire – in theory. GIs scanned the treetops and bushes with their binoculars for Viet Cong, enduring the humidity and the quiet anxiety one can only get on patrol.
The crack of a rifle in the distance broke the afternoon silence. A round pinged the side of the boat, and every soldier on board scrambled to find cover and return fire against the unseen enemy sniper. Another round struck the side of the landing craft. Nobody could find the shooter.
An American counter-sniper spotted the black-clad VC hiding among the leaves on top of a coconut tree, aimed his M21 and fired, taking out the enemy sniper in a single shot.
The American sniper was Sergeant Adelbert Waldron, who would go on to win two Distinguished Service Crosses for his outstanding skill and bravery. The legendary shot he made seemed impossible. He fired from a boat moving 2 – 4 knots (about 5mph) at a target 1000 yards away, a little bit over the effective range of the M21.
The optic he used was a technological wonder for its time: the Leatherwood 3-9x Adjustable Range Telescope (ART). A brainchild of Second Lieutenant James Leatherwood, this optic was attached to a base which raised or lowered the scope according to elevation like an iron sight. All a sniper had to do was insert a target of known dimensions into a bracket on the ART’s reticle and adjust the scope’s cam until the target fit inside the bracket. The scope would raise automatically raise or lower to account for elevation. Magnification on the ART was also made easier and quicker through the thumb nipple on the magnification ring. This meant US snipers would no longer need to perform math on the fly, trying to calculate holdover while the enemy rained down bullets on them. While this was a convenient solution, the problem was the ART would lose zero as it transitioned from target to target and would have to be adjusted every time it acquired a target at a new range.
Back in those days, etched reticles were a rarity, and even high-tier brands like Leupold used simple cross reticles with small variations. In fact, at the time, the Soviet PSO-1 scopes the Viet Cong were using featured a more advanced reticle than nearly anything in the west. Used by Communist Bloc designated marksman rifles up to this day, the reticle allows snipers to do no-math ballistic calculations thanks to features such as an etched rangefinder. This rangefinder diagram located on the lower left of the reticle allows the shooter to estimate the distance of a man 5’7” tall. It was also one of the first scopes to use a nitrogen filled tube to prevent fog.
We caught up with the reds a long time ago, and many modern long range optics feature a first focal plane reticle that simplifies range-finding without having to fiddle with a dial like the ART scope. For example, the Sightmark Presidio’s HDR2 reticle, designed for hunting deer rather than enemy combatants, is designed to determine range on a target of a known size without having to reach for a piece of paper for arithmetic in a similar way to the PSO-1, but with etched subtension lines that aren’t off center.
At a hundred yards, 1 inch is roughly 1 MOA. Knowing this, if, a target is ten inches tall but only reaches halfway to the lower subtension at max magnification, the target’s range is roughly 200 yards, since the distance from the center aiming point to the lower subtension line is 10 MOA, and the target would fit snugly in between the center aiming point and the lower subtension at a hundred yards.
In another throwback to technology that was popular in the bygone days, the Presidio mimic’s the ART’s thumb nipple with a throw lever, a trend which recently started to come back into style after years of magnification rings which were dial-only.
Over the years, the Presidio and other modern optics like it have adapted the PSO-1’s nitrogen-filled tubes and illuminated reticles while simplifying the process of range-finding that doesn’t mess with a rifle’s zero like the Leatherwood ART. These features, in conjunction with the Presidio’s high power magnification, truly make it an optic that builds on the laurels of its predecessors.