Is there any advantage of using the buffer tube instead of putting the recoil spring inside the receiver? Having a folding stock means you can have a longer barrel with the same overall length when in a vehicle. IMO that is a good thing unless you're breaching building often in CQB.
Based on my personal experience, folding stocks are not as useful as people imagine it to be in CQB or mechanized infantry setting. Between a overall shorter barrel or foldable stock, a shorter barrel helps with maneuverability much more than a foldable stock. (airborne troopers is another thing, which I have no experience in, so I won't comment on that)
Folding stock works in concept, since you can decrease the overall length of the gun significantly by folding up the stock. But it does not work well in practice. First, if you want the folding mechanism on a gun to be robust and reliable, it is often pretty difficult to fold the stock. I have 3 guns with folding stocks, a UMP, G36 and a VZ58. None of the foldable stocks on these guns, Western of Eastern, are easy to use. Of course, the stock on VZ58 is significantly more difficult to fold than the one on HK guns. I need to flip the VZ58 over entirely and push the pin using my palm to fold my VZ58. The stocks on UMP and G36 are a bit easier to fold, but the push button is so stiff that it takes quite a few seconds to push the button all the way in when I want to fold it. I often cannot do it in one push, and I work out pretty often...
What does this mean? If the folding stock is difficult to fold, then it is difficult to do it on the fly when you move through CQB environments or getting on/getting off vehicles.
I practice with my guns quite a bit at home, what I find is that reloading on the move is like 5 times more difficult than reloading when standing still. Essentially, any maneuver with a gun becomes 5 times more difficult when you do it on the move. If I am already having difficulty folding stocks on my HK G36 standing still, I am not gonna have an easier time doing it when trying to mount onto a vehicle or moving in CQB environments.
If something is difficult to perform, then in the field, the soldiers simply will not perform it. I am not gonna waste 10 seconds trying to fold my gun when I am getting shot at while trying to get into an APC, Imma just run in there with the barrel pointing forward and hope I won't get stuck.
Thus, folding stocks works really well in concept, but I believe it is a feature that is only properly utilized when no one is shooting at you. In this case, if you want to increase the overall maneuverability of the rifle in a tight space, shortening the barrel length makes all the difference, and my personal experience confirms this strongly. My UMP and VZ58 both have barrels less than 10.5 inches, and they work wonders in CQB, I never have to worry about poking the wall or door frame with the barrel when I don't want to. But when playing around with my 16 inch barreled AR-15, the barrel becomes a lot more difficult to work with when I try to move through doors and tight spaces.
So yeah, folding stocks sound nice, but their most important function is probably not gonna be utilized in the field when needed, simply because it takes too long and too much effort to fold.
Oh and another thing is that, when a gun is folded, you can't really aim and shoot with it. So redeployment of a folded gun also takes a bit of effort.
So yeah, I'm not gonna worry much about the QBZ-191 being non-foldable. The short barrel version should function extremely well in CQB and mechanized infantry setting, even if its overall length may be longer than a bull-pup QBZ95.
