The link will get you to the "Carding brush" section of the Brownells catalogue.
Please consider them an option,rather than a recommendation.I can't predict your results.
I've done some pretty nice rust bluing in a tank full of boiling water.After the parts are polished and degreased,they go in the boiling water.Then they are pulled out,and swabbed with a solution,then back in the boiling water.My first experiments were with "Mark Lee " Muzzle loader browning solution.
The point is,my workpiece then took on a uniform coat of rust.The "blue" happens when the rust is carded off with the fine,soft stainless brush.
In my case,noKroil,penetrating oil,etc was used.
I don't know for sure,but your "smooth rust" may card off to as natural of a patina as you will get.
Consider you can take the finest,deepest,most beautiful old school bluing and strip it off (ruin it) by a number of methods. Naval jelly,abrasive polishing,etc.
Thats starting over. Carding rust to blue is a naturalpart of rust bluing.
Take that for what its worth, and gently proceed your own way.For myself,I would not think of "removing "the rust,I'd think of carding it to blue.
Any etching/pitting of the surface will remain.Short of polishing it out and a reblue,thats just part of the historical patina.IMO,think"patina"
Gary's "rubbing with copper" is a tried and true method.
Turpentine doesn't exactly dissolve beeswax.It does soften it to sludge.I wanted to "seal" my new bluing with something after carding it.The beeswax/turpentine idea came to me. I rubbed it in warm,lightly wiped the excess,and let the turp dry out of it. I'm happy.
https://www.brownells.com/gunsmith-...ng-tools/gunsmith-carding-brush-prod6732.aspx
Just for clarity,I'm NOT suggesting you reblue. I'm pointing out that the rust you have is not so different than the rust stage of bluing.I suggest carding the rust rather than removing it.
It might be hard to comprehend if you have not seen it. My rifle came out of the tank red-brown rust.I carded it to a nice blue.You card off the red-brown.That leaves the lightly burnished "roots" of the rust,which is the blue