Tom as usual, there are many 'products' you can buy, that are not needed in the slightest.

Tinker is using the best black powder solvent, in my humble opinion. I do exactly the same and have been since I learned of it from a letter to a friend from the English, H&H, not the US MuzzleLoading barrel maker who uses the same name. Not sure how that works.

Until that time, I used very hot water and used to get minor flash rusting, just about every time I cleaned my rifles - which was about twice a week. It was quite upsetting to see that red rust come out on the drying patch.

I found cold water worked perfectly. By sticking the breech end in a bucket or container of water and flushing/pumping water up and down, forcing it out the nipple seat or vent, all the fouling would be disolved and flushed out the breech.

This cleaning is followed by running drying patches up and down the bore - I use cotton flannelette - ie; like baby diaper material. I use a jag size that allows doubling the cloth- it holds more and drys and cleans to the bottom of even deep grooves. It usually takes from 4 to 5 drying patches to get it bone dry. The last one feels sticky due to the bore being dry.

After drying, I flush/spray WD40 down the bore until it runs out the nipple seat or vent, then double patch and blast it out the vent, running that patch up and down the bore a number of time. The WD40 helps remove any residual moisture from the bore. I use that patch to wipe down the oustide of the barrel then put it back on the gun.

At Rendezvous, I will sometimes removed the lock and put a paper towel in the lock mortice, then stick a round toothpic in the vent and fill the bore with cold water, right ot the top of the muzzle and lean the rifle against the truck's mirror or a tree. About 10 or 15 minutes later, I pull the pic and let the water drain out. I replace the pic and fill it again, waiting then draining. I then run patches down and up the bore until clean and dry, then spray WD40 into it and flush that out with tight patches, wipe her down and that's that, clean the lock in water, spray it with WD40, wipe off the excess, then replace it - then store it upsidedown to keep the vent clear.

I then store the rifle or smoothbore, muzzle down. That way, any excess can run down the tube to the cloth the muzzle is resting on, and not form any residue inside the bore, as well as keeping the ignition area of the gun clear of wet oil. Storing the rifle, muzzle down, is a new thing for me, and in 20years of cleaning this way previously, I never saw any residue or varnish built up anywhere, from the drying WD40 as I've read happens. I think that's BS plain and simple. The main reason i store them muzzle down, is to keep the nipples, nipple seat or vent clear of wet oil.

Many people use and swear by various products and that's just fine. I use water as it works for me and everyone I know. Some folks say WD40 lacks good enough moisture protection in their areas due to normally high humidity. When I lived at the coast, I didn't have any problems - but do whatever you need to, to prevent rust.

I do not use black powder replacements as I feel they are harmful to the bore in the ML and they can destroy brass in BP ctg. guns.

In almost 40years of shooting black powder, I've never rusted a bore, inside or out, using real black powder. I did pit a bore and the outside at the breech from cap flash, using a chlorate primer compound I made from the pellet primer formula of the mid 1800's. It was somewhat unstable, btw and was outlawed in England in 1898.
Most of the modern replacement powders are made with one of the chlorates.