In my years in the military, and my times around guns, I have never once seen an AR with a rusted receiver. Never. (And believe it or not, sometimes those guns in the military were not treated with kid gloves.) When was the last time you saw a rusty or pitted AR? Do a google search for "rusty ar-15" and you dont get much back. I have read several of your posts about the 6940, and in my opinion you are underestimating their resistance to wear from normal use. Oil it properly and dont fret too much about it.