You do not need to remove the breech for cleaning. I have been shooting BP for decades and have never removed a breach for cleaning. Still shooting and cleaning the same guns the same way for over thirty years.
If not removed properly damage can be caused the the breach plug, barrel or tang or even all three.
Remove the nipple, place the breach end in a bucket of warm water and detergent, scrub with a bore brush, put a patch over the jag on your rod and start to pump water up and down in the bore. Dry after with dry patches til dry, run several patches with WD, spray the out side of the barrel, spray some in the barrel to drain to the bottom. Let it stand for a couple of hours on paper towel. Turn muzzle down over nite. 48 hours later bore wipe with some oil or more WD. Now clean.
Cleaned four guns each day for the last two days and back shooting them in the morning.