mkaye
If you are going to cast and shoot your lead bullets in your pistol they must be at least 1/1000 over bore or you will get gas cutting and leading. A bullet sized to .355, the diameter of the barrel, will tumble within 10 yards and cause leading down the barrel. Been there done that. I size all my 9MM .357 for that very reason.
The .452 molds will cast bullets in the area of .453 - .454 depending on your alloy and are meant to be sized down to .452.
When Ben sizes down his bullets 6/1000 he will reduce the diameter of his lube grooves as the lead shears off his bullets. May or may not effect accuracy. Personally I think you are not going to get the best performance out of your lead bullets by doing so but he apparently has not found this to be a problem.
You would be well advised to get a copy of Lymans Castbook Handbook and read it a couple of times. Most of your questions about casting lead will be answered.
Take Care
Bob