Some barrel steels are more prone to this flash-rusting phenomenon than others - I think 12L14 is on of the barrels prone to this.
A long-time friend of our almost ruined his 42" .40 cal custom barrel through religiously using boiling water- would not stop and ended up with pitting end to end. We lead-lapped it twice with abrasives embedded in the lap and it's better, but not back perfect, of course.
Since the mid 70's, I've been using cool or cold tap water for cleaning my bores.
First thing I do, is to remove the lock, using a toothbrush in the water, brush all the fouling from it. I wipe it off with a rag, and sometimes use air pressure (hose) to blast the residual water off - but not always. I set it aside to dry while I clean the barrel.
The barrel comes off the stock- pins, or wedges - no matter - and I use the toothbrush (my wife's
) to brush the fouling off the breech of the barrel (just kidding - I use an old brush
), then dunk the breech of the barrel in the water container. I usually use a 3 pound coffee can, 3/4's full of tap water.
After flushing the water into and out (breech in a container of water) of the barrel, perhaps 20 strokes, I remove the barrel from the water and wipe it dry with a towel. Them, I patch it out until dry. It usually takes 4 patches for this. I use a jag that is small enough to allow a doubled flannelette patch. Flannelette is the VERY best for drying or cleaning a bore. Thus, it takes 5 patches normally, sometimes 6 total for the whole job.
The last drying patch comes out clean - if not- repeat, but I've not had to repeat this flushing process - it works. I LIBERALLY spray WD40 down the barrel until it runs out the nipple seat, or vent - depending - then use the last drying patch to patch out the WD40. The first thrust with a patch blasts WD40 out the vent or nipple seat. You may want to drape a towel or cloth over that breech to prevent spraying WD40 all over the place.
I run that patch up and down, up and down until no further blasting out the vent happens - 2 or 3 times, then I use that patch to wipe down the outside of the barrel. That patch is ALWAYS pure white - clean! I again wipe moisture off the lock, then liberally spray it with WD40, then shake or blow that off and wipe, then replace. I will add here, that I lubricate the lock with silicone axle grease - the WD40 spray does not wash this off for several cleanings. When needed, I replenish the grease. I use synthetic as it is not readily washed off with WD40, or water, and it stays soft in freezing temps, when petroleum greases get hard.
