Apparently WD 40 is a water dispersent - so as an emergency holding operation - till you can flush out the badness with water - it is quite effective. Good old H2O is by far the best thing but it can be messy if you have your best shooting gear on and not always convenient.
I have to say it is great - even at my ripe old age to learn something new. I had never heard of bees wax for barrels but I can see the logic - I am sure it would protect them from rusting. Pretty difficult to apply to the inside but if it was warmed a little and applied with a mop I guess it would work. I suppose if it was all you had - and no one had yet invented a John Deere - not too sure where we are going with this one! Not too sure how lacquer would stand up to the wear on a metal barrel. As soon as it was chipped it would have to be repaired. I remember at school we would lacquer brass work in metal work class but it didn't last very long before it was damaged and looked awful. I still think that the traditional way of browning or blacking and an oily cloth is best.