Did great. I liked how they sprayed everything with brake cleaner, getting all oil and lubrication out, and then rapid firing it. Youtube comments always piss me off... "How about a REAL test and put 15,000 rounds of Federal through it"
I've seen these kids of tests and I will admit they are impressive. I watched a guy pour mud from a cow pond into the open breach of a Magpul Masada. He then swished the muzzle through the water to clean out the flash suppressor inserted a mag and fired the weapon. Impressive yes but... You could not pay me to pull the trigger on a gun that was that dirty.
These guys are brave to the point of being stupid. You only get two hands and one face. Pulling tests like this could cost you all three. If for what ever reason you feel the need to abuse your fire arm like this then get a vise.
I saw a test of a new AK (don't remember the brand but can probably find it). They took the rifle and dropped it in a slimy pond, pulled it out after an hour and all it did was spit out some mud and water with the first few rounds and kept on firing flawlessly. Not so sure an AR could do that, but it might.
Edit to add:
This wasn't a youtube post, it was a test result posted by an arms review site on their web page. I'll try to find it and post a link.....