I'm not a big fan of WD 40 for metal protection, Its great for machining aluminum, and will cut through dried oil/ grease crud. I suspect It's mostly kerosene with some light oil and stuff to make it smell pretty.
LPS3 is a very light oil (water thin) that is designed for corrosion protection.
On double barrels, I spray carb cleaner in the weep holes, get all that old crap out, followed by boiling in a TSP solution. Barrels then cleaned with greased lightning and Dawn soap.
After that double barrels are boiled in clean water to see how much oil comes off of them, if nothing comes out
Start your rust bluing process, if oil keeps weaping out..start over with TSP boil.
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