M85 tank machine gun


M85C tank machine gun on M3 tripod


Caliber    12.7×99 (.50BMG)
Weight, kg 29,5 (gun body)
Overall length, mm 1384
Barrel length, mm 1016
Cyclic rate of fire, rounds per minute Selectable, 400-500 and 800-950
Feed and capacity Belt   

In 1951, the US Army Ordnance Corps initiated a new R&D program to produce a new and improved .50 caliber machine gun for ground and tank applications. The new weapon had to overcome three basic shortcomings of the venerable “Ma Deuce” (M2HB) – an excessive length of receiver, a relatively slow rate of fire (for AA applications) and the need for routine headspace adjustments. Four weapons were put into development. In early 1956 Army Ordnance experts decided to concentrate further work on the T175 weapon, designed by AAI Inc., and development of the three other guns was terminated. At the same time a decision was made to concentrate on the tank version only, and leave ground applications for the old M2HB. The T175 was a great deal lighter than the M2HB, fired from an open bolt and had a fixed headspace. It also had a considerably shorter receiver. In the course of development, a new disintegrating link belt was developed, and in 1959 the T175E2 was adopted and type classified as the M85. This weapon was available in two versions, M85 (fixed, with solenoid firing) and M85C (flexible, with spade grips and a manual trigger).
Despite all of its merits, the M85 was found to have certain flaws and insufficient reliability, and its use was limited to the cupola mounts of the M60 main battle tanks.

The M85 is recoil-operated, air-cooled, belt-fed machine gun that fires from an open bolt and in automatic-only mode, with dual cyclic rates of fire available (a low rate for ground targets and a high rate for anti-aircraft work).
The M85 uses the short-recoil principle, with dual laterally-moving lugs locking the bolt to the barrel extension. A lever-type accelerator is provided in the receiver between the barrel extension and the bolt carrier. The barrel is of the quick-change type, and it is stated that the barrel change procedure can take only five seconds or so. The barrel is also fitted with unusual looking flash hider.
The belt feed is of the one stage type, using steel, disintegrating belts with open links (push-through type). The belt-feed module, which is powered by the recoiling barrel, can be set up to fire from either side.
The trigger mechanism allows for the installation of a manual or electric solenoid trigger. The low rate of fire is achieved by the introduction of an inertia delay mechanism, which is turned off to achieve high rate, usually to engage fast-moving airborne targets like helicopters or ground attack aircrafts.
There are no sights nor specific mountings available for M85, as those are provided by “host” vehicle.

: flexible-mounted version of the basic design, fitted with dual spade grips, a mechanical trigger and sights. Can be used from pintle mounts on vehicles or from the M3 tripod using special adaptor.