Weren’t those designed for a really fast barrel change ? Pull a pin and rock the receiver to one side ..... slide out the barrel and slide in the new, rck the receiver back and pin reinserted ....?
Yep, both the M73 and the M85 .50. I goofed and made some comments above that apply to the M85 and called it the M73, still having a bad taste in my mouth recalling the things.
The M85 was intended to be a tank cupola gun that could have an overheated barrel changed from the inside of the turret; same idea with the 7,62 M73 [and later M219 version; no better.] The previous M37 Browning .30 used in the M48 and very early M60 tanks [which had M48 turrets with 105mm main guns] was a great gun and reliable as any of the Browning-designed shooters, but you had to pull the backplate, withdraw the bolt and barrel extension, and unscrew and replace the barrel in its extension to swap barrels, then replace everything. It was a bit slow.
Not John M Browning's fault: he designed his machineguns to be watercooled so they wouldn't have a problem with the barrels overheating. Some of the WWI tanks used watercooled MGs, but none I can think of since.