Fouling is not caused by using 2Fg powder in a .54. Inadequate chamber pressure causes increased Powder residue. That is due to using the wrong diameter ball( too small, or too hard lead alloy) or too thin a patch and lube with the ball in the barrel.
This can be a "tricky " issue when working up a load for a given barrel, as molds from RBs come generally in .530, and ,535. There are not any " In-between" sizings of molds unless you have one custom made. Its important then to use CAST, Pure Lead balls in your gun, as the pure lead upsets in the barrel faster than the harder alloy lead balls will. If you are using Swaged lead balls, almost all of them are made with antimony in them, and they are much harder than pure lead balls will be.
I shot my .50 caliber rifle with the same .490 ball, and .015" thick patches, with very good accuracy, for many years. However, I was given a bag of .50 caliber Vegetable Fiber Wads( TOTW has them) and found that when i used a wad as a "Firewall", MV improved, SDV dropped considerably, Chamber pressure rose, causing more complete burning of the 2Fg powder in the barrel, leaving no more residue than when I was using 3Fg powders when working up loads for the gun originally. POI also rose at 50 yds by almost 1 inch! to my surprise.
I can deal with the POI by reducing the amount of 2Fg powder I use in my rifle. The lower SDV simply means the gun is more accurate, and I have fewer excuses for any " miss!" :shocked2: :blah: What I found to be wonderfully unexpected was the felt decrease in BP residue in the bore, when I cleaned the barrel after each shot( my habit). Even the amount of "gunk" on my dampened cleaning patches was visibly less than when I used the same Ball/patch/lube combination, Without the "firewall".
i am going to try a .495" diameter Cast Ball, again, and I am going to use some .018" patching I already have to see if I can get similar BP residue results without using the wad. The Swaged RBs I tried 30 years ago were simply too Hard to drive into the muzzle without cutting patches on the lands, then. I have since polished the crown of the barrel, and tapered the front of the lands at the muzzle to eliminate patch cutting there.