This is an ongoing battle, and it only serves to cause more confusion, I know it's confused me.
For years, since about the mid 1970's i always cleaned my rifle with the hottest tap water I could stand to put my hands in with dishwasher detergent, Then rinse with clean hot water, Then ran several dry patches till the patches came out dry and clean, Then I oiled with rem oil. In all that time never, never ever, Repeat never had a speck of rust develop in any of my rifles. If it has been sitting on the wall for several months i would probably run an oil patch down the bore and wipe and oil the outside of the barrel to remove the dust. But no rust, and no gunk in the bore either.
Now after reading all the alternative solutions to rust prevention and new formulas from kitchen products to High tech lubes. I am coming to the conclusion that do what works for you. If you have been doing something that prevents rust in your rifle, then keep doing it, why would you want to reinvent the wheel.
I recently read a thread here very well produced with illustrations and all, evaluating several after cleaning oils. I tried Ballistol one of the highly recommended products and have seen absolutely no difference from my hot water, dishwash, and dry and rem oil method that I have been using for more that 35 years.
Cold water will disolve BP residue, But hot water does it faster and I believe cleaner. The flash rust that people refference only happens if you leave the bore damp. If you don't leave it damp, no flash rust. I goes away with the oil swab. I think the hot water wash actualy aids in drying the barrel and removing any water that get trapped in the rifleing grooves. I truly believe its not what you clean with as much as how thourough and meticulous you are when you clean and oil. WD-40 is made to remove water but it leaves a residue that can cause gunk.
I yield my soapbox, thank you.