An old thread, but I'll throw my $.02 worth in
I shoot Rainier or Berry's .356" plated bullets through the gun, and it groups admirably. My load is either 5.0 of 231 or 4.0 of Clays. I shoot steel, so power factor's aren't a "factor"
I also use Remington nickle-plated brass, and use this brass ONLY in the 627. I never have extraction and/or loading issues.
I've experienced problems loading when I tried .357 jacketed & plated bullets seating the moonies all the way in. I use S&W moon clips exclusively