Sharps: I don't think it goes that way, but it is just IMHO.
I think the hot water expands the metal & opens the pores & the bore butter may go in there, but I also think the barrel cools & contracts & the air trapped in the pores condenses & you have trapped moisture in the pores of the metal & thus you have ceate a rusting enviroment. Who knows. I do know in over 33 years of ML'ing & having owned well over 50 ML'ers & built quite a few also, the ONLY gun I ever had rust was when I was regularly cleaning with hot water & used Bore Butter for rust inhibitor. Now this was 30 years ago & maybe I screwed up, but I have never used it since for rust inhibitor & know of allot of ol timers that will not touch it also for same reason. I always use plain ol cold tap water & just a small squirt of dishwashing detergent or a squirt of Ballistol.
One thing for sure, I know allot of people that started with Bore Butter & the likes & they have long left it behind as of rusting problems from trusting it.
The main thing is get it clean & get it dry BEFORE you put anything on it. Also, if you watch the steel under a microscope you will find the hot barrel when wiped clean & dry flash rusts almost imediately, where the cold one gives you much more time before the rusting starts.
As for Seasoning a barrel, works great when you step back in time to the 1700's & have no rust inhibitors & a cast iron barrel. IMHO, with the steel & rust inhibitors we have today, seasoning a barrel is about as useful as seasoning a barrel on a 1100 Remington shotgun. If you ever have a chance to go to a national ML match, look at what they are shooting. You won't see the fellers shooting seasoned barrels, & if by chance ya do happen upon one, he will most likely be leaving early. You will see them shooting spotlessly clean barrels.