If the question is 'are they safe',,that could end up being a 10 page thread w/still no ending to it.
There are people on one side of the issue that contend and have their facts and evidence that given a good set (not damaged, deeply pitted or thin walled) they are strong enough for smokeless powder loads "that mimic BP pressure curves".
Certainly the use of any smokeless powders is not in question here but it shows the big gap between the schools of thought as the other side can go as far as thinking that ANY composition bbl is to be laid up, never shot even w/ BP.
Composition bbls old and new are still accepted at the English Proof Houses for proof and reproof w/smokeless powders at normal proof and service pressures (no special powderpuff loads for these) . They are treated the same as a steel barrel.
Aside from their make up,,check for loose ribs. The old soft soldered joints can be weak and loose sections are not at all uncommon. Laying a section back down can be an easy quick job,, or it can be a frustrating experience because of the old encrusted dirt, oil, rust in the joint.
Re-laying the entire top and/or bottom ribs is sometimes easier than trying to 'fix' a section of loose rib at least for me. It's just a soldering job.
At least w/the ribs off you do get to check things inbetween the ribs. Sometimes the old use of acid type soldering flux makes for a deeply pitted to the dangerous point in there. I've had a couple that were scrapped after a look inside there and these were steel barreled hammerless doubles.
As far as refinishing them to bring the pattern back out,,any of them can be re-done successfully. You can have the older traditional Brown & White colors of the muzzle Loader era and English cartridge guns. Or the Black & White colors that many of the US shotgun makers used.
It's a matter of rust browning vs rust bluing.
The trick if it is one to bringing out the pattern in the steel & iron entanglements that make up the bbl material is an etching process in between the rusting cycles.
Ferric Chloride in very weak solution is what I use (>5%). A quick dip plunge into the stuff and that's it.
No carding wheel here,,all steel wool carding and done under running water right as they come from the etch tank.
It's a very long process as you remove the color from the harder steel in the pattern with each etch cycle, but leave a bit of it clinging on the softer iron.
The amount built up w/each pass on the iron in the pattern is very small as you take part of it off at the same time you clear off the steel.
15 to 20 passes is not unusual for a 'damascus' finish. The first 5 or 6 will leave you thinking nothing is happening.
Bores have to be protected during the entire process because of the etching. Plugs I don't trust. I coat the bore heavily with shellac,,recoat at cycle 8 or 9. Never have had a problem.
Brown&White is faster to do as it skips the boiling process each time needed to do Black&White.
Some have good luck etching every other or every 3 cycles instead of every time. Same with the boiling doing a Black & White pattern,,some boil every other cycle.
Takes some experimenting. Some bbls will allow you to get away w/short cuts if you want to call them that. Others won't. You know quick enough if you can,,like the Blue converts but still has a brown tint to it if you try and skip cycles. Stuff you learn.
There's other ways and techniques,,this is only one.
FWIW..
A quicky way to bring out the pattern is to apply laundry bleach on a cloth to the freshly polished bbl(s). No heat,,just scrub them down. Sometimes amazing results occur,,sometimes another hour of polishing for you to rid you of the mess of what could have been.
Always rinse the stuff off completely,,leave any on the surface (or it gets inside the ribs),,heavy rusting will occur.
