The M39 EMR (Enhanced Marksman Rifle) was developed from the tried-and-true action of the original "M14" Battle Rifle of 1959, itself a further evolution of the World War 2-era M1 Garand automatic rifle. The M14 saw considerable service in the Vietnam War as well as operational service throughout Cold War Europe and across the volatile Korean Peninsula. As some 1.5 million of the type were ultimately produced, the weapon can still be found in quantitative numbers in inventories today and private owners appreciate the types fine qualities.
With its origin in check, the newer M39 shares much of the same qualities of the M14 before it including its gas-operated, semi-automatic firing action as well as being chambered for the 7.62x51mm NATO standard cartridge. The M39 is, in essence, a further evolution of the M14 series itself, extending the operational life of the decades-old platform for the requirements of the new battlefield. The designator of "Enhanced Marksman Rifle" indicates its primary use by "non-sniper" elements, operators more akin to the "designated marksman" in the US military (also known as "sharpshooters" elsewhere) - a battlefield element tied to a long range, repeat-fire weapon intended to serve as an integrated part of the infantry squad. The M39 EMR was developed for use by the United States Marine Corps (USMC) and replaced the M14 Designated Marksman Rifle (M14 DMR) in the same role beginning in 2008. The M14 DMR itself served from 2001 to 2010 and saw combat action in the 2001 American invasion of Afghanistan and the 2003 American invasion of Iraq.
The designated marksman role falls upon an operator to provide accurized ranged repeat firepower at the squad level. This differs from the traditional dedicated sniper element for the DM is not officially rated a sniper per se ("Scout Sniper" in USMC nomenclature). As such, the designated marksman is provided slightly different tools for the role - a weapon developed more to fill the void within the squad that is already stocked with automatic assault rifles and squad assault weapons (SAW). In the case of the M39 EMR, the DM is given a proven combat rifle firing a full-power rifle cartridge - a quality the American assault rifle lacks (this being chambered for the 5.56mm cartridge). Optics allow for the precision required of long-range engagement.
At its core, the M39 is a highly modified version of the original M14 series though the basic M14 form can still be identified despite the changes. The receiver contains all of the critical internal working components as well as an ergonomically shaped pistol grip. The trigger mechanism is slung under the receiver and set just ahead of the pistol grip. A safety is fitted ahead of the trigger unit. The metal stock is adjustable for the use and includes an integrated cheekpiece for comfort. The straight-box magazines common to the M14 are retained in the M39 and fitted in the normal manner at the lower front of the receiver. As such, the charging handle is also set to the right side of the receiver as in the M14. The forend of the M39 gives the weapon its distinct look over that of the original solid wood body of the M14. The M39 sports a perforated and ribbed forend designed to accept accessories as needed. A collapsible bipod is, therefore, standard. The forend shrouds the low-set gas cylinder to which the barrel is set above. The barrel protrudes ahead of the forend and is capped with a noticeable slotted flahs suppressor and forward iron sight. The M8541 Scout Sniper Day Scope (SSDS) sight is standard issue but the receiver's Picatinny rail support can accept any compatible device. In all, the M39 certainly looks the part of designated marksman rifle though - thanks largely to its M14 lineage - can be utilized as a service rifle/battle rifle should the situation require it.
The internal action of the M39 utilizes a gas-cylinder to "tap" the pressure from the preceding cartridge being fired. This pressure is used to chamber a new cartridge into the chamber, made ready for firing, and achieves the desired "repeat-fire" characteristics found in many of today's automatic weapons. The gas action is tied to a rotating bolt locking mechanism to which a rate-of-fire of 60 rounds per minute is possible - certainly an edge over the bolt-action facility common to traditional sniper weapons. The weapon is fed from a 20-round detachable box magazine chambered for the 7.62x51mm cartridge. Muzzle velocity is approximately 2,840 feet per second. Effective range is listed at 850 yards giving the USMC DMR quite the "reach" on the modern battlefield.
While the M39 has certainly lived up to its expectations in the field, the system does maintain origins in a 1950s Cold War-era design. As such, the USMC evaluated and ultimately adopted the newer, more modern M110 Semi-Automatic Sniper System (SASS) with introduction in 2008, leading the M39 to have something of a rather short operational service life within the branch. The M110SASS is manufactured by the Knight's Armament Company and shares an outward resemblance to the Colt M16 assault rifle. Like the M39, the M110 is chambered for the full-power 7.62x51mm NATO rifle cartridge. As of this writing (2012), the M39 is still in operational service while the M110 works to gain a foothold in the USMC inventory.