What ever happened to letting them hit the ground while you load another? Take a knee, grab a new mag out of a pouch while releasing the spent one, load it up (so you can get back in the fight) and put the spent one from the ground back in a pouch. this way, you can fire with one hand, while the support hand does the work.
But hey, that's just me. But the carge pocket works well if you don't want dusty mags. Use it in the same manner, with the pocketing replacing the dropping.