"It seemed that dirt simply didn't affect this weapon."
The mud/sand/dirt/ceracoated-water-beetle tests are usually done on gun forums to show the AR fanboys that the AK family of rifles is more reliable in "dirty" environments. I mean, AK rifles are used in dirty deserts by dirty people all over the world, and that's why they're so reliable, right? Well, the reason AKs are used in poverty stricken countries is because they're so cheap to buy and easy to manufacture, not because they're any better than any other family of battle rifles. I don't bother qualifying that claim because there's nothing to qualify: you won't find dirt poor militants fighting other dirt poor militants with FN F2000 rifles in dirt poor countries because they cost like $2,800, not because you can't bury one in dirt and expect it to fire. Who buries their rifle in dirt, anyways?
Did you know that the M16 has a dust cover over the ejection port to prevent sand/dirt/mud/throwing-stars from getting into the action? So does the AK-47. Weird. Now considering that, take a looksie at the receiver of a M-14 or M1 Garand. Oooooo, there's no dust cover. Do you think you could sling mud over the top of the action and have it fire without jamming? Maybe it'll fire once or twice without jamming, but sooner or later it's going to. Oh, CTone, everyone knows about the hell-and-back reliability of the Garand and M14! Nothing can stop them! I'm telling you that if you introduce foreign matter into a firearm's action -- any firearm -- it will not fire for long without a stoppage. Likewise if you throw firearms out of airplanes; just because your gun survives a fall doesn't mean that it is airplane-drop-proof, it only means that it didn't hit the basketball sized rock six inches beneath the grass, and nothing more.
Wanna guess why military training and CONOPS don't include any procedures for running over or burying weapons in sand/dirt/mud or freezing them in a tray of mashed potatoes? Because it's universally accepted that it will probably induce a malfunction when the weapon is fired. I've never browsed an AK technical manual, but I doubt it will tell you that the gun is immune from jamming due to sand/dirt/mud/3/4" ball bearings, and I would bet a shiny nickle that it will tell you to keep the action clear from any obstructions, to include water. Internet fanboys love pictures of SEALs, Rangers, and Recon Marines with painted faces coming up out of the water with their rifles at the ready, but what's not well known is that unless the gas tube of any rifle is clear of water, it will blow to smithereens if it's fired. I bet there's a technique for not getting that to happen. And sure, I've seen Elite Team Fighters dunk their favorite brand of rifle in a bucket of fluoridated tap water and then fire it without issue, but curiously I've never seen one of them pop out of a submarine in 50 feet of water and swim two miles to the shoreline, at night, while submerged, and then fire it two seconds after breaking the surface. I just haven't.
Don't get me wrong, I love to see weapons tortured to see how tough they are. But being a realist, I don't put much money on tests that try to show some resistance to foreign debris being forcefully transported either directly into the action, or right on the entrance of it, and then firing without a jam. I also don't place faith in tests where an AK is fired out of a cannon. You're basically only showing the favorable part of statistics. The torture tests I like to see are ones like this, where an off-the-shelf production pistol is subjected to a lifetime of ammunition over several months, and lives to tell about it. I can tell you that the only malfunction I've ever had in an M16 or AR type rifle combined was shooter induced. I've actually found that as long as an AR rifle stays reasonably lubricated it will run like a sowing machine without cleaning for a long long time.
Me personally, I like to keep the nastiness out and off of my weapons. They run better that way. I don't clean them as often as I used to, but I make sure they stay lubed up with 10w50.