The issue with the mini and dirt is that the primary dirt-sensitive bearing surfaces are pretty much on the outside of the rifle (the two forward bolt lugs and the round camming nub that engages the slot in the operating rod). When mud or sand of the right consistency gets on top of the receiver and works its way into the bolt lug recesses and the op rod handle slot, things can grit up really quickly (you can feel it just by working the charging handle slowly).
One big reason for the AK's legendary reliability when dropped/buried in mud is that the design works very hard to guard its bolt lugs from mud and debris. The safety/selector/dust cover seals the ejection port, and even if it is left open the bolt carrier wraps completely around the top of the bolt and prevents it from being exposed to the elements. The bolt lugs are down in the receiver where you have to work to get at them. And even with all that, the designers of the AK *still* emphasized to keep the rifle buttoned up tight in dusty conditions, and lubricate, lubricate, lubricate to keep any fouling fluidized.
I think
this document is a translation of the Soviet AK-47 service manual. It contains the following instructions regarding use of an AK in the desert (page 132).
50. USE OF THE AUTOMATIC RIFLE IN AREAS WITH HIGH TEMPERATURES AND SANDY TERRAIN
In training exercises, during matches and in combat in sandy terrain, it is necessary to adopt all measures for protecting the rifle and ammunition from dust.
During extensive use of the rifle in dusty terrain, the bolt and the guides in the receiver should be oiled frequently through the opening for the magazine and ejection port; the rifle need not be disassembled for this operation. Before reloading the rifle after each oiling, the functioning of the firing and trigger mechanism should be checked by pulling the operating rod to the rear and releasing it several times. In such dusty terrain, the opening in the receiver through which the magazine is inserted into the rifle should be uncovered only when changing magazines and during the period lubrication mentioned above. In combat, the slot for the cocking handle should be covered during lulls in fire by means of the selector cover plate, i.e., by setting the rifle on safety.
The rifle should be cleaned and lubricated after each extensive use. Special care should be taken in cleaning and oiling the working surfaces of the trigger and firing mechanism, bolt, operating rod, extractor, gas tube and magazine.
In combat, lack of time may make it permissible to fire the rifle without oiling it, but not without wiping the dust off all the parts. The rifle must be thoroughly cleaned and oiled at the first opportunity.
Not coincidentally, the AK instructions are *exactly* the way to keep an AR (or a mini, for that matter) running reliably under the same conditions, except that you squirt the oil in the gas vents of an AR rather than in the ejection port and magwell like you would with an AK.
I dare say that in adverse conditions in WW2 or Korea where mud or blowing grit was a factor for M1's, M1 carbines, or M14's, soldiers probably did their best to keep the receiver openings protected from the gunk (wrap it, keep the receiver tucked under your arm, whatever) and cleaned and oiled them as often as they could. I note that the Garand, M1 carbine, and M14 were
all issued with oilers so that soldiers could keep the bearing surfaces well lubricated, and it was not uncommon to issue every soldier both oil and Lubriplate grease for that purpose.
