Just recall that there are two shooting areas in driven grouse, in front and in back, with a VERY careful but fast turn-around with the gun lifted to the sky as you turn. You can get sent home if you violate this, and so you should. So the shots in front are longer then shorter and the ones in back are shorter then longer. All this makes special choke set-ups a bit problematic. Shots are low and fast as they come screaming in over the heather. I have shot most of mine behind, as they tend to surprise me as they come in. Better shots kill most in front.
In any case, relatively open chokes work for me.
