Copper, graphite and even moly can cause galvanic corrosion. Fortunately, we're dealing with an anodized aluminum receiver and nice smooth high carbon or even stainless steel, sandwiched together with a generous schmear of grease.
See: "Effect of molybdenum disulfide on electrochemical corrosion of metals":
http://www.springerlink.com/content/n17r4hvq646j0g43/
I generally march to
NASA-TM-584, which does not forbid copper but does warn against graphite. Note that TM-584 references MIL-STD-889, specifically for dissimilar metals.
If you think aluminum-steel interfaces are bad, you ain't seen nothing. Be glad few gun parts are made from titanium.