Help with a new knight
I don't know about the stock. The Knight will shoot B209 just fine with the red plastic discs, you could also go with a bare primer breech plug. You just have to use a hot primer, like CCIM or similar.
Re: Help with a new knight
Be careful with BH and heavy bullets. I saw a guy shooting 100gr BH and 500gr bullets and the RPJ could not hold up - it wasn't pretty neither was the accuracy. I believe you'll be better off with their bare primer set up.