The M85 machine gun was well-known by soldiers of my generation, especially tankers who used it in the M60 series tanks. It was a belt fed, recoil operated heavy machine gun that fired the .50 BMG cartridge. It was lighter than the M2, weighing 65 pounds.
It mounted in the command cupola of the M60 series tanks and was considered the commander's weapon. It used a push-through belt, unlike the pull-through link belt used by the M2. The gun did not have the familiar butterfly trigger of the M2, but fired either by pulling a handle on a chain, or by a solenoid attached to the elevation handle.
The M85 didn't make the jump to the newer M1. The Army said that it was unreliable and maintenance-heavy. Although I never had any issues with the gun. The ones I used ran fine. The commander's cupola had an optical sight for the gun, but most of us simply stick our head out of the hatch and watched the tracers
In my opinion, the M85 had two major drawbacks. First, it used a link system that was not compatible with the M2 ammo system. Same cartridge, different links, so the crew had to be sure that they were drawing the appropriate ammo from the ammo point. Second, it was a gun designed to be mounted in a vehicle. It simply did not have the versatility of the familiar M2 Browning.
The ones I used ran good. If the tank commander took the time to align the gun with the optical sight, it was very accurate, but most of us simply watched the tracers.
I looked for a YouTube video of the M85, but can't seem to find one. It was pretty much out of service before YouTube was invented.