I have the exact same gun in both the 6 1/2" barrel and the 8 3/8" barrel. I purchased the Bianchi AccuMold (or something like that). It was about $30 but worth every penny. It's a black synthetic type material that is molded in shape to hold the RB perfectly still. It also has the snap on the top of the holster, and I think that Bianchi calls it a "thumb snap." I used it on a hog hunt this year and it was very easy to take out in an emergency (which I kinda had as a hog was coming right at me.
) It is a high quality product.
I was VERY satisfied with it and highly recommend it.