Staff Writer (Updated: 8/31/2016):
The original M40 production mark was simply designated as the "M40". These were identified by their single-piece, all-wooded stocks and standard Redfield 3-9x scopes mounted over the receiver. After warping issues of the wooden stocks became apparent, the "M40A1" mark was introduced which featured the McMillan A1 fiberglass stock and a stainless steel barrel. The Redfield scopes were also dropped and replaced by Unertl types. The "M40A3" appeared in 2001 with a new McMillan Tactical A4 series fiberglass stock and a switch to Schmidt & Bender 3-12x50 Police Marksman II LP scopes with their illuminated reticles. A Schneider Match Grade SS #7 barrel was also introduced and other changes to this mark drove the weapon's overall weight up by approximately 2lbs. These rifles appeared in time to participate in the American invasion of Afghanistan prompted by the events of 9/11 and have been used extensively since. In 2009 there came the latest M40 incarnation - the "M40A5" - which introduced support for the AN/PVS-22 series night vision scopes and detachable box magazines (as opposed to the original's integral box method).
Overall, the Remington M40 mimicked the lines of the original M700 complete with its long-running stock making up the forend (forestock), receiver, pistol grip and shoulder stock. Later production shoulder stocks were padded for some comfort while a rear sling was present along the left hand side. The trigger, protected by an oblong ring, was unobstructed under the receiver. The bolt-handle and ejection port were set to the right side of the body. A second, forward sling was set along the forward-most portion of the forestock to the left side of the body. The barrel was exposed across the top of the forend and appeared more or less smooth and featureless. An optional bipod could be affixed to the forward portion of the forend for stability when tracking/firing. Sights were conventionally mounted over the receiver and there were no backup iron sights present.