I've never heard or read about doing this so just asking the question. Everything I've seen talks of plugging both ends. Seems that as long as you can remove the black oxide, you should be good to go?

Definitely no; you don't want any "oxide" in your bore, which is rust. Having said that, since you don't actually put the acid in the bore (unless you are using the fume blue method), then the damage/rust in the bore will be minimal. Still, most do plug the bores so they don't get any rust in them.

In doing external surfaces, I've been able to get a pretty darn smooth finish after carding. My thought was that as long as I didn't let any pitting occur, it might not have any ill affects on the bore.

I've read of some old time gunsmiths that would apply varnish in the bore, let dry, and then rust blue. Removing varnish afterwards was easy with solvent and a brush.

Yes, I have heard of using varnish too. Point is, that any oxidizing of the bore is not a good thing; I have had customers who refuse to have a barrel even salt blued because it still oxidizes the bore. On a hunting rifle, I don't think it matters, especially since, as I said, you are not applying acid to the bore. I do plug them before boiling.

If you apply solution by swab to the outside of the barrel only, then there will be no rust in the bore. I used to coat the inside of the bore with lacquer and then remove with lacquer thinner. I tried it a few times without and found no difference.


Bob
www.rustblue.com

quote:

Originally posted by dpcd:
Yes, I have heard of using varnish too. Point is, that any oxidizing of the bore is not a good thing; I have had customers who refuse to have a barrel even salt blued because it still oxidizes the bore. On a hunting rifle, I don't think it matters, especially since, as I said, you are not applying acid to the bore. I do plug them before boiling.

Don't the plugs pop out as the air inside the barrel heats up?

Here are some practical observations after 35 years of rust bluing and hot caustic bluing.

Rust bluing: I started out plugging the barrel but quickly learned it wasn't practical. The plugs either leaked or got stuck a lot. Like bobster I found out that that the bore did not rust as long as you kept the bluing solution confined to the outside of the barrel and dried it with compressed air while it was hot from the boiling water cycle. I also used distilled or rain water to deter rust.

Caustic hot blue has no detremental effect on bores at all. I have witnessed some rifles shoot under 1/2 moa with hot blued bores. I always used a boil out cycle, blowed the bore out with compressed air and submerged in oil over night. With caustic hot blue running temperatures of 285 to 300 degrees it would be very dangerous to plug the bore. Almost garunteed to blow a plug and a geyser of 290 degree caustic salts erupt everywhere.

I have had a lot of barrels blued and don't know what was done to the bore. I always clean them after a light lap with JB.

quote:

Originally posted by Craftsman:
Here are some practical observations after 35 years of rust bluing and hot caustic bluing.

Rust bluing: I started out plugging the barrel but quickly learned it wasn't practical. The plugs either leaked or got stuck a lot. Like bobster I found out that that the bore did not rust as long as you kept the bluing solution confined to the outside of the barrel and dried it with compressed air while it was hot from the boiling water cycle. I also used distilled or rain water to deter rust.

My sentiments exactly. I've rust blued maybe a dozen rifle barrels and several double shotgun barrels and carefully fitted tapered wooden plugs at first. Invariably the plugs popped out or pulled loose and boiling water migrated into the bores. I found that a couple dry patches run through the bore immediately after removing from the boil left them pristine. Now I look upon the plugs as being handy holding devices and don't worry about hot water migrating inside. After all, we're only a couple generations removed from routinely using hot water as a bore cleaning step to remove corrosive salts.

Yeah, I have had the plugs leak but it doesn't seem to matter. They do make good handles. Salt bluing; never use plugs there.
Couple generations? I still routinely use hot water for bore cleaning; corrosive primers and black powder. Water is the US Army approved solvent for black powder fouling; "Pour a gill of water (warm if it can be had) into the muzzle...".