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WD-40 does protect from rust well but it attracts dust and dirt. I would just use lube meant for guns frog lube for me!
WD-40 is to a gunsmith like candy is to a dentist. I used to make alot of money off hunters that would just spray WD-40 into the actions of their shotguns, the stuff eventually turns to a gummy varnish and can stop O/U's from switching barrel and slowing auto and pump stikes enough to get unreliable ignition. Spray it on the outside if you feel you have to but use a good light gun oil for the insides. Johnsons paste wax works realy well for protecting your shotgun in salt areas, just wipe it on and don't buff it.
F10und3rzThat was a great link, pretty much covers everything on auto oils and WD-40 and a great reference for finding GOOD lubes.Thank You
Mobile 1 works good.