All I ever used on My ML's for almost 20+ years was Bore Butter. As you stated and I too gave them a Hot Water Bath then they were treated with BB. Since reading this ForumI changed to MX BC and MX Gun Oil. I have only treated my New Never Shot ACCURA's with the MX Products.
My first clean with the MX BC was done on my ACCURA, and the MX did have dirty (gray) looking patches after I cleaned the bore, a few more patches and they were spotless, mabey it was the oil applied at the factory that came out of them.
After reading this I got 2 of my older ML's that I have'nt shot in over a year (and both had the hot water bath, cleaned, then treated with BB and stored) I hot watered em, to remove the BB, then ran a patch of MX BC down the bore and they were clean. I DONT have the MX CS so I cant say for sure if just the MX BC did a good enough job to remove anything as I dont think it's a cleaner, just a conditioner? So I guess I'll get some MX CS and see if it pulls anything out of them.
I know some of you dont like the BB, but I have never had a problem with rust or flyers. But I usually only shoot most of my ML's a couple to a few times and then there cleaned and treated with BB. I dont go on marathon shooting seassions with them so mabey that's a reason for them being so clean too. And all I have ever shot out of all my ML's are sabots so mabey this is another reason for the barrels being clean.
I'll get some MX CS and reclean them 2 ML's and see if anything comes out and let you all know.But after using the MX BC and MX Gun Oil in my ACCURA's they come cleanalso so we'll see. As stated above by bronko, mabey the advantage of MX is just helping the occasional flyer and crud build up and fouling problem.BP