Not much to add as Blue nose pretty much nailed it (Except I follow up with fluid film). However, I will add that, cold - Luke warm water is all you need. You can buy solvents or add soap or whatever and that won't hurt but you won't gain anything over straight water except a cost. I have been shooting BP since the early '80's and my Dad (now deceased) since the early 70's. Have tried many "trick" cleaning solutions and nothing we have tried has outperformed plain water. I have limited experience with BP cartridge, in fact only maybe a few hundred rounds of 12GA but when I was loading those, I would roll the edges of the fibre wads in liquid bear grease (same as I do for my ML shotguns) to help each subsequent shot to clean some of the soot from the previous shot. It is my belief that if you load your fibre wads dry, residue buildup will get much worse and may even get to the point of increasing pressures after several shots. I also loaded my shot shells similarly to my ML shotguns, leaning towards square loads (equal powder/shot by volume). While I have a bag of paper hulls around here somewhere I have never loaded them. I just loaded plastic hulls I got from a trap shooter friend. I cut the star crimp off and loaded them with a roll crimper. Yes they get small holes melted in them but this does not contaminate the chambers in any way and I just shoot them once and throw them away. Interestingly, (to me) of the several hundred shells loaded this way (straight from the trap range to my loading bench ) only a small handful would not fit the chambers of the guns that I was shooting them from. Probably should have checked the fit before loading them. In case anyone is interested, after determine the length of hull for the load I was using and the roll crimp, I cut a piece of electrical conduit too the appropriate length as a gauge, them would slip it over the new-to-me hulls and cut them off across the conduit pipe with a knife to achieve a square mouth of consistent length.
