Gotta go with the dirt, but I dont think its necessarily a gas system problem. Check the extractor, though.
S-can the mags, try with known good mags. Use brass-cased milsurp ammo (no Wolf crap).
Check the headspace for good measure.
The autonomic nervous system provides for involuntary muscle function - the work of breathing, digestion, and so forth. On some folks, that's a pure waste of ingenuity.