Originally Posted By: Evil_LurkerThe inside of the barrel will be "in the white" even if it's blued or parkerized. You seal the bore and chamber when you finish it.
I'm not sure I'm reading this right, but if you're saying that the barrel and chamber are "plugged" before bluing you've obviously never done, or seen any bluing done.
I worked at a small gun factory when I first retired and I can tell you for positive that the bore and chamber aren't "plugged" and DO get blued right along with the rest of the barrel.
The temperature of the bluing tank is pretty high. Even if you could seal the barrel somehow, you'd have a pipe bomb on your hands. You don't want Janet Napolitano knocking at your door, now do you?
Firing a few bullets down the barrel removes the bluing, hence the need for rust prevention inside the bore.
FYI,,, Bluing is simply controlled rust. Ceracoat, Norrels, and the like are an entirely different process.
I have no experience with these so I won't comment on them.
Edit; I have heard of Gun Restoration Experts pre-heating barrels and then plugging them before blueing, but it was second hand information, so it may or may not be true.