dark bores and rust bluing

[mrussel]

Ive seen many people ask what causes a dark bore and hear many answers such as pitting or oxidation. Some people even assume that a dark bore IS pitted. In fact,its often asked "How do I clean up a dark bore" and invariably someone comes back and answers "There is no way to clean up a dark pitted bore". Certainly a dark pitted bore is not something that can magically be made to go away. On the other hand,Ive seen several smooth dark bores with sharp deep riflling.
  It occurred to me today that there is a process called rust bluing. The way it works is you allow,or cause a thin even coat of rust to develop. You then heat the part,usually in hot water to about 100C. The red oxide turns to a black oxide. You then "scale" the part with a wire brush removing any loose oxide on the surface,and repeat the rusting and heating until the desired depth of blue is reached. Im certain that this is what makes many dark bores dark. (The oxide answer IS in fact the correct one in many cases,but the way it probably happens is sort of interesting) This is probably why some dark bores are nice and smooth still rather than pitted (although some ARE pitted). What I think is happening is the bore gets a coating of rust on it due to neglect and then is heated when the firearm is used turning the red oxide rust to black oxide. It also occurs to me that one poster claimed to have made a dark bore shine using bluing remover. This makes perfect sense. The potential pitfall of course is that a single drop on your finish with leave a big bare metal spot. I usually leave the bore as is,just cleaning it up. I dont think that layer of oxide is going to hurt anything,but if I decided I had to do it (now that I think I know what causes it,maybe I will on something that has no finish to speak of already) I would cover the gun from top to bottom in crisco or lard or some other thick grease to try to protect the finish,then run over the bore with an ammonia based cleaner afterwords and then hose the entire thing down with a can or two of walmart brake cleaner.

[MnMike]

This makes sense to me. I have seen some very nice and smooth dark bores.

mike

[trotterlg]

When a new barrel is blued it is blued inside and out, it only get shiny when the bluing is worn off.  There is nothing at all wrong with a clean dark bore.  Larry

[mrussel]

When a new barrel is blued it is blued inside and out, it only get shiny when the bluing is worn off.  There is nothing at all wrong with a clean dark bore.  Larry

 I have had guns from the factory that had blued barrels but the insides shined like mirrors. I guess some do it that way and some dont. That brings up an interesting question though. If you have a gun with a smooth dark bore,shouldn't it get better with use as the oxide wears off.

[Dances with Geoducks]

The dark bore comes from years of corrosive primers being shot through, not cleaned and left that way.

You can buy the WWII military cleaner for a buck or two any most gun shows or online.
It will take the dark right out.

It is nasty poisonous, so wear a mask and gloves. Ive done many folks rifles with my can, and it makes them look like new.
Ive yet to see any pitting in them.

[Mikey]

Dances:  are you talking about the old GI Bore Cleaner, of which I have about a lifetime supply..........