So regarding here and locked thread -- in the video, the issue is one of it not firing due to not going into battery... They didn't verify that there were any issues with the fcg getting fouled, or with the weapon being unable to cycle with all that crud.
The top cover served a squeegee to dump all the crap from bolt carrier into the receiver... Had they repeated this test like with other weapon systems where they cleaned out, buried, and then rinsed off the bolt carrier before firing -- as anyone with the least amount of sense would do -- it likely would have fired... Not unlike the Funker tactical test posted earlier...
Actually, or further, I find MACs tests far more realistic than InRanges... It takes a special kind of neglect to get a weapon that InRange dirty and expect it to perform. To cross say a stream or creek and get your weapon submerged or crawl through a wet ditch and do the same, the sediment and whatnot in that water would be similar to a MAC test. And yes, those types of approaches would be common in patrols or other combat maneuvers... InRange's strikes me more as a WWI trench warfare type of abuse scenario where both you and your weapon in are in a constant state of complete filth, recognizing that all foxholes can get muddy yet soldiers manage to keep their weapons clean...
While I can't see into the action, I can say with a high degree of certainty that the crud must have been blocking the firing pin and/or not allowing bolt carrier to continue forward to point where primer and firing pin aligned.
Why?
B/c the out of battery safety is also the f/a trip lever that the ATF foolishly (in regards to weapon safety) required to be removed (two sears in standard configuration -- f/a trip lever releases/deactivates the right "auto" sear when in semi-auto mode so that the striker/linear hammer can be released with the semi auto
sear when the trigger is pulled; the left, s/a sear is deactivated in entirety in f/a mode. By my understanding, the weapon
should fire out of battery due to how most VZ58s are converted to semi-auto...
In regards to Horse's comment -- ARs are typically manufactured to tight tolerances and clearances, whereas AKs often are manufactured to looser tolerances and clearances... That said, tolerances reflect the range in which a weapon will function as designed and clearances are the amount of space to allow stuff to work its way out, also as designed... Bottom line, Horse is right on terminology.
Personally, though not correct, I usually think of clearances as features like sand cuts on Fal bolts, and tolerances as features like the wobble between an AK bolt and receiver...
Back to my original point -- clearances (properly used) do matter; however, other design components can compensate for those clearances. Mike Pannone has written a few good AR reliability pieces for Defense Review. In those, he discusses how heavier buffers and recoil and extractor springs help to account for fouling in tight clearance ARs... Here's the best one where he ran a BCM AR over 2.5k rounds w/ no lube and just spring and buffer upgrades:
http://www.defensereview.com/the-big-m4-myth-fouling-caused-by-the-direct-impingement-gas-system-makes-the-m4-unreliable/Heavier bolt carriers on AKs and VZ58s work similarly to adding heavy buffers to ARs... And AKs have xtra power springs available, but the VZ58 does not insofar as I'm aware...
Further in regards to clearances, AKs have large clearances on pretty much all components... VZ58s have tight clearances between the BCG and upper receiver, but looser clearances for the bolt itself (until it locks into battery) -- the VZ58 also lacks clearance cuts on bolt carrier rails, but bolt can push stuff back into the receiver and down into the mag well via it's locking tab cuts and a limited amount forward... The amount of crap in the video obviously exceeded the clearance/self-cleaning clearances designed into this weapon system...