I've not got it in front of me, but by memory its a series of open meetings, the Welsh, Aldersley, British Championships Bisley, and some others, the top so many in an aggregate of those will shoot in a final and I can't remember where that is. I'm not sure but I doubt you need to enter "the series" but do the individual meetings and probably tick a box, I thought its also in classes.
Look in the new Rifleman which is just out and should be sat at your club, its a full page not far into it.

I can't find it on the NSRA web site, but then they can't even put their own regs on it.