That's been my experience anyway...
I take it you never used the M73 or M219 co-axial machinegun, happily replaced in tanks by the much better M240C, and also quite usable by ground troops, though a couple of pounds heavier than the M60 MG. I was first blessed with the 3 of the things as a headquarters company tank section gunner in the mid-1960s, and by stripping two of the guns for their newest parts, could usually keep the third running for a few 30 round bursts, at least. During gunnery exercises, we'd swap that working gun between the 3 tanks, but that might have been a little difficult in the real world. Though compact and fitted with a nice quick-change barrel setup, the things were junk.
I'm no fan of the M9, either, but at least they work if kept spotlessly clean, and so long as they aren't dropped on the left side grip, which tank crewmen tell me happens often. [It's the left-side grip that's exposed in a tanker's shoulder holster] But it seems their aluminum frames hold up to a diet of 9mm rounds no better that the German's aluminum-framed P1 pistols of the 1960s did, having been *improved* with a steel reinforcing bolt behind the barrel locking flap late in the design's life, before being replaced by the H&K USP 9mm handgun. The Austrians, of course, changed from the P1 to the plastic Glock 17 when the shortcomings of their aluminum-framed handguns became apparent.
