In honor of being declared the “blog of the month” over at The Firearms Blog (TFB), we will be posting about tank and afv related small arms this month. A few days ago we posted about the not so successful M73/M219 7.62mm coax machine gun. Today we will be taking a look at it’s larger cousin, the M85 .50 cal machine gun. Much like the M73, the M85 had a very mixed reputation among US tankers. It was intended to replace the venerable M2 .50 cal machine gun which had acquired an excellent reputation throughout WW2 and into the post war era. However, the M2 was considered rather heavy and bulky for use inside the enclosed commander cupolas common on US postwar tanks. By the time the M60 MBT was introduced, the M85 went into service, mounted in the commanders cupola/turret. The M85 was also used by the Marine Corps in the LTVP7. The M85 was almost 11 inches shorter and 20 pounds lighter than the M2 and featured a quick barrel change option and two different rates of fire. The M85 could be configured for either left or right hand feeding and in its tank gun configuration was fired by means of a solenoid. The M85 gun suffered from a history of reliability problems which it was never able to shake. By the time the US adopted the M1 Abrams MBT in the 1980’s, the M85 was replaced by the gun it was originally designed to supersede, the M2 .50 cal. Oddly enough, while the M85 and M2 both fire the same .50 cal round, ammunition for the two weapons is not interchangeable due to the use of different style belt links. According to globalsecurity.org, the USMC has in storage 3 million .50 caliber cartridges loaded in belts designed for the M85, despite the fact that they removed the gun from their inventory, replacing it on the LTVP7 series (now designated AAV-P7)with the M2.
PS Magazine article on the M85 (Issue #146 1965)
PS Magazine article on the M2 .50 cal (Issue #168 1966
Tank and AFV News 
The Marine Corps continues to store about 3 million . M85 machine gun, even though the Marine Corps has removed the M85 gun from its inventory and no other weapon system uses this type of .
LikeLike
Yep, the links are different. The M2 pulls the rounds out of the back of the belt, a design going back to WW1 when belts were made of fabric, same with the Maxim. After desintagrating links were invented it was possible to make a much simpler feed system with the rounds simply pushed forward into the chamber .This started with the MG34, continued with the MG42, M60, M240 down to the M85.
LikeLike
I know both the M-85 and the M-73 were manufactured at the old Springfield Armory in the late 60’s after the government run facility closed and manufacturing contracts were given to GE Weapons Division, headquartered the “Underhill Facility outside of Burlington, VT and the maker of the famous Gatling and Mini guns. During that time, the M-85’s were under constant inspection by DECAS because of a “Fail to Feed Over” (FFO) that were sometimes blamed on the links catching the gun body at the entrance of the body of the gun or the ammo chutes and extractor problems that resulted in the fired round not being pulled from the chamber and the new round staked in back of it. The new round then absorbed the extreme heat of the hot test. Several guns were damaged due (and one employee in my memory) the resulting cook off, especially during the 1000 round hot test done at the conclusion of the 10,000 round acceptance testing done on every months’ production run. The M-73’s seemed to have far less problems. Obviously, neither gun’s problems were ever resolved.
LikeLike