MPAR-556: The Homecoming of AR-18
Eugene Stoner’s AR-18 design is a textbook example of how an unjustly neglected construction may return in its full glory after years of modifications and improvements. Although considered much better than AR-15 by many, it was newer officially adopted, but it served as a model for development of almost every modern assault rifle of today. The last sprout is MPAR-556.
In its own time, it was considered as an alternative to AR-15, that is M16. The basic differences could be boiled down to operating principle and the price. Although both rifles are gas-operated, AR-15 uses direct impingement, where the gas from a fired cartridge is directed into the bolt carrier or slide assembly to cycle the action, while AR-18 uses a short-stroke piston. The latter solution is much more reliable since parts last longer and overheat less. Also, it doesn’t call for such a thorough and frequent cleaning.
What is more, its manufacture process was much cheaper than AR-15, due to the mass use of deformed and spot welded sheets, without complicated procedures like pressure casting and milling. Despite all these advantages, it has never replaced AR-15 in the US armed forces. One of the reasons was that its full auto mode was somewhat unreliable and required further refinement. This didn’t stop constructors to experiment and use this system in many newer rifles like Steyr AUG, SA-80, SAR-80/RS-88, Howa Type-89, Bushmaster M17, G36 and almost all western rifles of today.
On trials for Australian Army’s new assault rifle, which would replace the obsolete L1A1, the main competitors were Austrian AUG and Australian-made AR-18, designated T2 and produced by Leader Dynamics. The winner was AUG, which was then produced in Australia under the name of F88. T2 Mk5 was produced as a semi-auto rifle for the civilian market until 1996. The American company “Masterpiece Arms”, which became famous for its M10 and M11 machine pistols, based its MPAR-556 rifle on the Australian model T4.
The rifle uses the short-stroke piston operation with a rotating bolt with three locking lugs. The bolt carrier is prismatic and it slides on two rails, engaged with two return springs. What surprises is the manufacturing process, which is unusual for the newer weapons – stamped sheets technology. Western manufacturers have never really adopted this technology introduced by the Germans during WW2, when large amounts of guns were needed at a low price. The upper receiver is made of a rectangular steel tube. The two halves are connected by a single pivot pin. All these features sum up to the recognizable boxy shape, which rounds the overall tactical look.
The barrel is 406 mm long, which is a standard that keeps the best ratio between the compactness and the weigh on one side and the accuracy and effectiveness on the other. With the new 5.56 mm ammunition types, the 406 mm barrel is more than enough. Instead of more common hard chrome plating, the barrel is carbonitrided. In this process, the steel surface is diffused with carbon which has deeper penetration, and nitrogen which diffuses at lower depth and at the surface. This way, the surface is hardened in depth (carbon) and ever more hardened on the surface (carbon and nitrogen), together with increased corrosion resistance (nitrogen).
The bolt handle is located on the left side of the receiver and it doesn’t move while firing. The pistol grip and the controls (fire mode selector, magazine release) are identical to the AR-15. The rifle is fed standard NATO 30-round magazines. The stock is collapsible in the right side.
In the field of sights and tactical attachment, MPAR-556 is on terms with the competition. Two standard Picatinny rails run on both sides of the forward grip and on the receiver top side. Additional rails are installed on the left and right sides of the forward grip in different configurations. They can accommodate a number of sights, flashlights and grenade launchers. Everything combined, an empty MPAR-556 weighs 3.54 kg, which is average for its class.
The rifle was announced by “Masterpiece Arms” on the Shot Show 2013. The production started by the end of 2013 and for 2014 a new variety was announced featuring a more powerful 6.8×43 Remington SPC caliber. The main target buyers are hunters, although it would excel as a sport rifle or a home/ranch defender. The hopes are high that it will also draw attention of law enforcement agencies and hopefully, armed forces. All in all, MPAR-556 is a rifle which combines modern solutions with the cost effective classic ones.