Here is a thread that compiles the results from a number of informal corrosion preventive tests.
http://thefiringline.com/forums/showthread.php?t=508243
http://thefiringline.com/forums/showthread.php?t=508243
I've oiled them lightly and wiped all oil off and I have also tried leavings thin layer of oil on them... Regardless they still rust
You MAY be oiling the guns too much. I know that sounds crazy but too much oil traps any moisture between the barrel and the oil film causing rust to form under the oil covering.