SKS: What is the rebound disconnector's use?

In the SKS trigger group there is a secondary disconnector, usually called the rebound disconnector, part 50 in the drawing.






I've been scratching my head, but can't find a straightforward practical reason for this "extra" part to be there.

Searches brought up that the rebound disconnector was not part of the initial Simonov design, and was only introduced after a few years of production. The only reason given is "Well, they put it in for a reason, so there must be a good reason. Just leave the darn thing alone". Fine and good, but "someone must know" is not enough for my innate curiosity...

I tore apart a dozen trigger groups, put them back together with all parts, with less parts, without springs, in short tried anything I could... And still did not see what was the point of this secondary disconnector under normal use.

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 lower hump pushes the trigger bar below the sear, thus disconnecting it, and allowing the sear to intercept the hammer upon cocking. Rinse and repeat.

On this picture you can see the trigger bar and sear through the inspection hole: this is after firing, with trigger still depressed; the trigger bar is below the sear.




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???

Here you can see the hammer when the bolt is retracted, pushing down on the rebound disconnector's ears. The trigger is pulled, showing that the trigger bar slides below the sear, disconnected.




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, and more hands than I have to still be able to take pictures, but then you can create a slam fire.

So, from what I understand, the trigger group is perfectly safe and functional without that part, unless a purebred imbecile is at the controls.

Am I missing something?

The basic Russian foot soldier in the late forties was not PhD material, could it be that Stalin had a clumsiness problem with his infantry, hence the rebound disconnector's glorious appearance?

edwardware said:

I know nothing of SKSs, but this:


I think you solved it and don't recognize it. If you watch high-speed video of a semi rifle operating, you'll notice many exhibit quite a lot of bolt-bounce. With the wrong combination of springs, ammo, and recoil control, the bolt can bounce 1/4 of the way back, probably enough to create the hammer-follow you note as possible.

Click to expand...

Wondered about that too, but when you fire, the trigger bar is disconnected by the hammer and can't go back until you reset the trigger. There is no real time to do a half-reset and push the sear away during a bolt bounce... Not that it's impossible, but so highly unlikely that it would have been of no concern.

For the Russians to add one part, increasing costs and complexity, there must have been a real-life problem.

I've never read of an identified issue with the early Russian SKS, at least not one that would be related to that.

edwardware said:

Milking the trigger in combination with insufficient recoil control will half-reset the trigger. This is essentially bump-firing. With enough recoil, bump firing is a minor geometry/spring rate tuning away in most semi-autos. I think your mystery part's purpose is to prevent that.

Click to expand...

zaitcev said:

You're missing the role that the recoil plays in this. It's possible to hold an old SKS just poorly enough that the motion of the gun under recoil makes the soldier exert "just the right amount of pressure on the trigger". The rest happens as you envision.

Click to expand...

I'd agree with that... Can't see any other reason.

So, basically, that rebound disconnector is there to prevent human error (AKA moronitude).

It would be interesting to find old USSR records in regard, but Uncle Joe was never one to put too much info into the public domain...

carbine85 said:

You might ask these guys http://www.sksboards.com/smf/index.php.

Click to expand...

I had first posted on that site, got only one response in total...

I found out that I get more replies and interaction here on THR than on brand/type specific sites. Had the same experience with HK-related questions: I got answers here faster and better than on a HK fan site.

THR!

lysanderxiii said:

Right there is the answer, there was some combination of things that happened (probably as described above, or that the sear was being damaged) that occurred in the field that made the SKS go full-auto.

Click to expand...

When you just lost ten million men in a war, and sent to the Gulag the thinking ones among the remainder, what you're left with is not the best of the litter... Add to that the new AK47, which relegates the SKS to rear echelon and reserve, weeding out any notion of fully trained or even trainable elements, and you get a "good combination" of things to start getting this sort of problems on a noticeable scale, I'd guess.