Thanks Greatguns. Still not sure I grasp why it's needed. Here's my thought process after studying the firing sequence extensively and the trigger group function:
When the bolt is not in battery, the primary disconnector is at its upmost position, letting the trigger bar rest against the housing's sear rails, thus preventing the trigger from actuating the sear.
Once the bolt has fallen into its locking recess, the disconnector pushes down on the trigger bar, which can then actuate the sear if needed.
Upon firing, the hammer's cam pushes the trigger bar below the sear, thus disconnecting it, and allowing the sear to intercept the hammer upon cocking. Pull the trigger and the process repeats.
The rebound disconnector only comes into play when the bolt is retracted: in this position the hammer is beyond full-cock and depresses the rebound disconnector, which pushes the trigger bar below the sear... BUT the trigger bar is already below the sear, having been disconnected upon firing!
So, what's the point???
The only time the rebound disconnector would have any use, is if someone tried to manipulate the bolt while holding the trigger, which is a stupid thing to do anyway. I can see where, if things were just right (or just wrong, rather), the sear could be pushed out of the way and the hammer left hanging on the primary disconnector, which would result in a hammer follow, and possible slam-fire.
This can be demonstrated by simulating the sequence: cock the rifle slowly, putting just the right amount of pressure on the trigger, and without pulling the bolt fully rearward to avoid the rebound disconnector doing its job and disconnecting the trigger bar. It takes attention, but then you can potentially create a slam fire.
So, from what I understand, the trigger group is perfectly safe and functional without the rebound disconnector, unless a purebred imbecile is at the controls.
Am I missing something?