Originally Posted by chromados
For my Pin Cask I usually prime it with 5 ounces. I would worry about dry hopping it for that long as you will start to get grassy flavors from having the hops in contact with the beer for that long. If I dry hop a cask I usually consume it around the 3 week period.
I don't know if it's common practice but I know a local brew pub that dry hops with different hops in the cask. They drop the hops in fill it, bung it up and let it sit until it's on tap. I haven't really tasted grassy flavors.