The finish on your gun appears to be S&W's standard "brushed stainless." My guns might look more polished but don't forget, they've been handled, shot and cleaned for over 30 years.
If the cylinder faces on my 617s are any indicator, you will not hurt your gun's finish on that area if you get aggressive with the cleaning. The only places I do not use a brass brush on any of my S&Ws is on the smoother outer surfaces. There, I use a normal nylon toothbrush if a rag wetted with solvent doesn't do the job.
As a side note, the fouling from some powders is harder to remove. Bullseye, with Unique a close second, leaves a sticky black coating on your gun and hands that if left on the gun overnight, is a bear to remove. Titegroup is dirty but not sticky. I use Clays powder for all my target loads in .38 Special, .357 Magnum, .44 Magnum and .45ACP. Like any powder, it also leaves some fouling but it isn't sticky and cleans off easily.
If you don't handload, you can try different brands of ammo to see if one burns more cleanly than others. I can't help you there as I only use factory loads in my .44s and then only for hunting, so I only fire a round or two every year and that's only if I'm fortunate enough to get a deer within handgun range.
Ed
