i try to gravitate towards "the simple", which sometimes ain't so simple, and then i ditch that and attempt to get even simpler.
"fresh" bp residue is readily tepid water soluble. that's a fact. it might take as long as 5 minutes left in the touch hole plugged barrel to work its magic. a concoction cleaner might do it 5 seconds. that's the beauty of most concoction bp cleaners - speed and efficiency of use.
"not so fresh" bp residue is a horse of another color. that can get dissolved with plain water AND a buncha patched jagged elbow grease. a good concoction will clean that out in, oh, about 15 seconds.
"not cleaned for a day or more" can be a nightmare that plain water won't fix easily - if at all. this is where a concoction cleaner is a must-have. hey, why in heck didja wait so long? you must have a death wish for yer gun.
this is why i "moose milk" before leaving the range/woods, and follow up with plain water whence back at the ranch. if i'm smart. then i don't need no concoction cleaners.