I asked a question so his meaning is clear. Why didn't you say the same thing to Lee?

How about you stop starting crap?

Try the JB compound but not the steel wool. I had a rust spot in my Knight barrel too. The JB didn't take it out.
But I found a simple non-abrasive solution. Get a can of Evaporust, remove the breech and plug it up (I used a rubber cork from the hardware store), and pour the Evaporust filling the muzzle. Don't get any on the outside. If you do wipe it off.
Let it set in the barrel overnight (24 hours). Pour out and swab the bore. Your rust will be gone.
PS: make sure your plug is not leaking because the Evaporust may remove or tarnish the bluing on the gun.

MD54,

OK, there are those who just love 209. However, its not perfect. I get that. What I'm wondering is why we hear so little about Black MZ? Apparently it loads volume for volume with regular blackpowder, similar pressure curve, but soft and not real corrosive fouling. Its not flint-friendly, but supposedly if you start the load with a couple of spritzes from your pan primer, it lights off OK. What do you know to be wrong with this powder?

OldBob

The chemical make-up of BH 209 includes both Potassium and Sulphur. Given enough time and moisture it will rust your bore.

Adding those two extra BP ingredients and the equivalent volume measure was the only way General Dymanics could get their smokeless/progressive burning powder listed as BP sub.

With all of that it is a great powder by overpriced.

I can assure you, in 10 days of hunting in Colorado there's no sign of any rust in my Ultralite. I've left BH209 in my gun for the full two weeks of Buck season in PA with no signs of rust. I've never even come close to seeing any kind of rust on stainless Muzzleloader's. I also used to load 777 in my Encore for a week of hunting and never seen rust. So will it rust, I'm sure in time ecspecialy if you don't take care of your ML and don't use a good preservative in your barrel. But nothing I ever need to worry about and most shouldn't either ecspecialy with BH209

I am a 99% T7 shooter which is well known to be more corrosive than BH, and again in SS - GM barrels - oh and in Docs White rifles I have never had a corrosion problem. And I do not clean the rifle until the end of the season even after shooting POI check shots at the beginning of the year. I have complete faith in the bore treatments I use and the techniques of barrel care I have developed over time. BH concerns me even less than does T7.

I am not sure what may have deveopled in the bore of the rifle in the OP's post. But since the growth is probably located in the area where the bore enters the stock - I am concerned about some form of water or water vapor problem. maybe not even related to what ever type of powder he used.

So you didn't have rust with a clean barrel, is that what you are saying?

Yes, I have seen rust with bh209 before on a couple different guns. They all had one common denominator, they were blued. When I first started using bh209 I had a stainless barrel. I left stainless barrels dirty for awhile (at least a month on one occasion) and did not have rust. So, I thought you could do this with any gun with bh209 and was in for a little surprise when I did this with a blued gun. I told my father in law he could do it too so he got rust in his gun. Lol. This is just my experience and I will only do it with a stainless gun but I still keep an eye on it.

Man I seriously don't see how you guys go without cleaning your rifles. I physically CAN'T not clean mine!!! My OCD would beat me to within an inch of my life if I tried! That's ANY firearm not just my MLers. My carry pistol is cleaned every day. Walk in, break it down, give it a loving wipe and bore clean, lightly oiled, reassembled, and according to which one I carried that day, is put in it's little "spot" somewhere throughout the house for quick access if needed.

That's dedication......you are going to wear that thing out.
I hear you on needing to clean. I have a modest amount of guns in a climate controlled safe. I will get the "urge" to go right through the safe and thoroughly clean them all several times a year. Once I start to think about it I will get a nagging feeling that I need to check them all out. Love the smell of gun oil almost as much as gun powder.