An AR builder of good repute is telling folks to use brake caliper grease (non-metalic) to coat the recoil spring and end the dreaded "sproing". Well, I went overboard on one of mine. All of a sudden it would not feed worth a hoot! Others of mine seem to work ok. I finally was told by another armorer not to do that ! I cleaned it off and I'm back to fine feeding. He said to use a light oil and listen to the sproing. This is a public service from me to you . LOL at my expense.