Well, assuming that all is well with your 27-2 now before -ANY- ammo goes through it, understand that you are holding (arguably... and we do!) the largest and most stout .357 Magnum that Smith & Wesson ever made.

As long as your ammo is .38 Special, .38 Special+P or .357 Magnum from a SAAMI source, then there is no ammo that will hurt your revolver, assuming the ammo is exactly what it is advertised to be.

Unfortunately, there exists no holster that I have ever heard of that won't, over time and use, leave marks on the gorgeous polished finish of a Model 27. However if your revolver isn't mint/unfired/NIB, then don't sweat the small things and carry it, shoot it, LOVE IT and don't worry about it.