Beware, WD-40 will also dry to a gummy varnish unless cleaned off often.That's what my dad used for years 30 wt. applied with a shaveing brush. His guns did not rust and seemed to work ok. My self Im a WD40 man displaces water and sprays into the hard to reach places.
I have a Browning .308 BLR (older Belgian) and had used WD-40 for years, one day the trigger simply refused to work. I flushed and scrubbed it with WD-40 (it's own best solvent) followed by carb cleaner, then oil. The trigger once again worked perfectly.