I would buy 10 rounders. I finally got to shoot mine the other day and it is a lot of fun to shoot. The magazine worked fine with 357 or 38 spec, but I had done just a little bit of filing at the front end.
It was pretty cold, and the factory mag was very difficult to remove when empty. At room temperature, it will start to fall out a little where you can grab it and pull the rest of the way, but it was pretty hard in the cold. Not enough weight to drop free. An extended round magazine would aid greatly.