No bore cleaner would be safe on barrel black.
An effective bore cleaner will be a combination of components to aggressively remove powder, lead, plastic residues etc.
Barrel black is an iron Oxide coating, and would be effected by all bore cleaners.
Rust is Iron Oxide
Barrel blue/black IS rust - there are Ferrous Oxide and Ferric Oxide - one is red rust Fe2O3, the other blue/black rust - occurring in nature as the mineral Magnetite Fe304. The red rust is a powder and falls off the barrel, so the process keeps eating into the metal. Blue/Black rust forms a hard outer surface and therefore stops further oxidisation. Rust remover removes both types.
Selenium di-oxide based cold browning / bluing solutions both appear blue in the bottle. The additives are different, giving a differing "tone" of the colour. Original finishes , called hot caustic bluing, have differing end tones from brownish , through bluish, to jet black according to how long / temp they are baked. Pure SeO2 leaves a dark grey tone, and the additives are to "blacken up" or "brown down" the tone a bit to better match caustic finish colours. The difference is small in the end finish. Generally cold blue/black is used on steel, and brown on white metal / brass bits etc where the alloy / metal is oxidisable
Musket browning solution is cellulose based oil, where the volatile evaporates are heated away leaving a translucent light brown finish. Can be used on any metal as it's not a chemical change to the surface, but a residue left covering it.
While the bore of a gun is an exact definition, unfortunately the chamber size and rim in the extractors or ejectors is manufacturer defined.
Also, over time, the ejector slides wear and cartridge / snap fit may change.
Wear and outside tolerances means carts or caps may drop though ejectors, conversely new guns or tight tolerances on the ejectors can mean that snaps may stand proud.
If it’s the OD that’s too large, gently filing off a few thou will allow them to drop into the rim machining in the ejector. If they are already in, but standing high because the rim is too thick, remove the striker in the snap and use coarse wet & dry - 120 grit or thereabouts to take a few thou off the snap's face. Finish with a finer paper. Should only take 5 mins.
Alternatively, but it will be trial and error, Megaline only make alloy snaps, but Bisley, Napier etc also make these and their tolerances may be different - and may make them also in either plastic or brass as well as alloy.
We do not hold these in stock, and they are more expensive, and we can't g'tee first time fit in your gun - so I suggest you either grind a few thou off or return for a refund. If you buy Bisley from us ( we can supply to order) or Napier from Napier, you may still have the same problem.
Basically the aim is to bake the oil onto the metal leaving a hard cellulose film.
It's the same process as some Woks and similar are finished with.
Poor result will usually be associated with either preparation cleanliness ( prepare with 0000 wool and isopropyl alcohol) or correct heating temperature.
Many of my products require skill. Master gun makers might take 5 years to learn all the processes from another master.
Novices can expect to have to experiment to learn - so trial and error on scrap before finishing the final product.
Good thing about this finish is that it can be removed, - heat is up to soften and 000 wool back to metal. Clean off with Isopropyl and start again.
All you need do is soak the barrels for 5 mins or so - squirt it down the barrel and roll it around to coat it. Or you can plug the end of the barrels and fill them to the chamber - pour out and re-use several times over recovered fluids.
When its soaked, scrub with a wire brush, patch out. Check if residues clear and repeat if not.
This is called blushing.
The cellulose paint is reacting with water, usually just atmospheric moisture from high humidity.
Water may also be present in the wood.
Clean the sanded stock with white spirit. Dry it out well on a radiator or direct sunlight.
Test that the cellulose or thinners are not contaminated ( shouldn’t be, but test to eliminate this possibility) by testing the finish sequence and preparation on a separate piece of scrap walnut or other hardwood. If the cloudiness does not occur on another piece of wood known to NOT have had a previous finish, the problem lies in the stock's preparation - moisture is coming from the wood. If the same effect is duplicated, it is the humidity of the environment in which the work is being done, or some water has got into either the thinners or the lacquer. This usually separates and can be seen, so the good solutions can be decanted off drops of water that will be under the lighter cellulose or thinners.
90% of finish issues lie in the original rub down quality, removal of all previous residue finishes, and removal of water in or around the process.
Other causes can be:
A/ over diluted with thinners
B/ in very hot conditions the thinners may be evaporating too fast - you can slow down the thinner ( retard it),by adding white spirit to the much faster and lighter thinners to slow the dry time.
C/ applied over a non-cellulose grain sealer Shellac goes under on oil/wax finish, while cellulose finish has a dedicated sealer.
Cellulose grain sealer, how-ever, works fine under oil finishes as well as cellulose lacquer.
It should be baked on in an oven.
The principle is to evaporate the soluble fluid content and leave the raw cellulose. This is a transparent yellow thru brown coating. End colour depends on temperature and no of layers.
A blow torch simply burns it off to no effect.