M60 seems very weak when ACE is loaded. After firing some bursts into the M60 in general, the turret will jam and smoke start pouring out. The commander turret in particular seems quite vulnerable to this. In fact, the effect can be recreated with a Katiba if you aim there.
Video reference below. While there are some mods loaded in the demonstration, I have confirmed multiple times that the same result happens when only CUP and ACE are loaded.
It appears this may be an ACE ammo cookoff thing going on, but I'm not sure exactly how that works.