Good stuff, all - however - hookie - WD40 does not cause rust. It might not prevent rust in humid areas, but it does not cause rust. If it did, all my guns would be rusty - yet none have ever rusted the borers - the oldest being about 30 years old - maybe a tich more. never any rust, and the only after cleaning oil I use, is a flush with WD40, which is patch-blasted out the nipple seat or vent, then the gun is wiped down with that patch and that's it. One was stored, untouched for about 8 years - no rust inside nor outside, same as the ones used more often - no difference. It's all I've used since moving North from the very much more humid South of BC, about 1976.
I take it you meant due to the high ambient humidity in your area, the WD 40 didn't protect against rust.
In reading G. Hall's post, makes me wonder about phony powder useage - or - the bore might have a fissure problem - or - he's just not cleaning to the bottom corners of the grooves. G.Hall - you say the bore is bright and shiny - aren't the grooves? They should be just as bright and shiny - if not, that's why it's rusting. Lapping might help, but with all the previous rust, I think a properly cast lead lap is in order. A cast Lapp won't take off the corners of the lands, as will cloth, leather, rubber or other material that must conform to the bore if used heavily. The lead lap fits the bore perfectly and thus removes minute amounts of metal more evenly than something that is swaged tightly against the top corners. If the barrel had deep rounded rifling, I'd have at it with all sorts of stuff, but since it's probably .010" to .012" deep, I'd cast an adjustable Lapp on a rod and do a proper lapping job.
