exterior metal staining

[magnum loader]

I shooting a new S&W 627 satin finish SS 357mag. My problem is brown staining on my cylinder exterior & other close by metal parts, especially after going thru 100-200 rounds. Tightgroup powder seems to be the worst about making this stain but I also use Unique & Win296. I've tried some gun cleaners, auto carb. cleaners, solvents, & ordered that expensive Mpro-7 cleaner that S&W told me would clean my staining away, it did a real nice cleaning job on the bore but won't budge the staining. I know I can't be the only shooter out there with this problem. I have not tried abrasive cleaners since my finish is a glass bead satin, the abrasive cleaners would end up polishing the metal, that would be a disaster.HELP!