Is it not just decided day by day?
If you find out any knowledge could you post up as we're in the area over the weekend. I think Franco Cookson was in touch with the estate to try and get some info out of them that could go on the RAD.
By the way, the knowledge is that the shooting is of deer using rifles, so the range of danger is loads more than you'd expect from a grouse shoot - if the sign is up, don't go.