Greets,
DISCLAIMER:: I am far from an expert on this subject, these are just my observations and opinions::

I have 2 percussion firearms. One is a CVA Navy Colt revolver, in .36 caliber. And the other is a Traditions Hawken Rifle with double triggers, in .50 caliber. I bought the Pistol as a kit, assembled it ( with many mistakes, but I finally got it right. ) I used Hoppes solvent for years on it.. then I bought my Traditions. I got a water soluable black powder solvent for it. I now use that for both guns... It cleans up the black powder ( or pyrodex, only 2 I haveused ) quite nicely! Lead fouling is not really an issue, I assume because of the low velocities generated in my pistol ( I can see the ball going down range if I stand to the side while someone else shoots ) and the fact that I shoot only lubed conicals ( Rarealy ) and patched round ball ( no lead to bore contact ) out of my rifle.
I presume after reading the ingredients of the solution I buy, that soap and water would work nicely as well, however I havenever tried it. I will say this.. IF you shoot Black powder or black powder substitutes from a firearm, then use black powder solvents or recomended substitues only!!! ( IE Soapy water )
That freinds is the bad side of experience talking!!!

Just my uneducated opinion!
Terry