You posted the same thing on THR and didn't like the answers you got so after the thread is locked you come over here and ask the same question. I'll offer the same evidence here. These guys abused a G21 far worse, and documented it over a period of years and thousands of rounds. Not just one day and a few magazines.
http://www.survival-spot.com/survival-blog/glock-21-torture-test/
They did all the same tests plus:
*Buried the gun in dirt and sand with the slide open and closed. Not just closed.
*Immersed it in salt water for a week.
*Dragged it behind a truck on both grass and pavement.
*Shot the slide 10 times with a 22 rifle.
*Dunked it in both baby powder and bead blasting media which is much finer than sand.
*Dropped a loaded gun and magazine from the roof of a house.
*Dropped the gun from an airplane at 500' elevation and 100 mph into a field.
The only failure the Glock had was after being dropped loaded from the roof of a house. The tester placed a primed, but unloaded cartridge in the chamber to see if the gun would discharge along with a fully loaded magazine. The gun did not discharge, but the ammo in the magazine was deformed by the landing and would no longer chamber. The gun didn't fail, but the ammo did.
And yes, he placed both a G21 magazine an HK magazine in a bucket of sand just as the Mak was tested. The HK and Mak failed, the Glock worked.
Both the Glock and Mak performed very well, better than most, but I'd choose the Glock for many reasons. The exposed hammer on the Mak is the weak point and where it failed by allowing dirt between the hammer and firing pin. The lack of an exposed hammer, and the enclosed magazines on the Glock do a better job of keeping debris out of places where it shouldn't be. And these tests prove that.