Interesting comments. Thanks. No question about being over optimal weight. I'm wondering what the appropriate tradeoff is between weight and finish in this event (as is probably everyone else who's ever flown this). I notice that plans for some past winners/record holders seem to strike a nice balance between weight and finish (see, for example, the plan posted on the NAR website or the plan in my copy of the NOVAAR competition handbook). Polished tubes and sealed, airfoiled fins seem to be a must here. The plan on the NAR website has an empty mass of 8.5 grams (although this has a shorter payload section than required for today's NAR payloads). My son's unfinished rocket weighed up at 8.9 g and mine came in at 10.4 g (sprayed with primer and wet sanded with 600 grit sandpaper). Clearly I've given up some weight, but my Cd should be lower. If we get a hole in the rain I'll find out on Saturday whether the tradeoff was worth it (I'm hoping so, or a certain 10 year old is going to be impossible to live with).
Another dilemma with this event is the availability of parts. Nose cones for T-20+ size tubes are almost non-existent out there. At a building session, Mr. Brown of QCR showed us one approach where you cut the payload section short so that the payload protrudes from the front and acts as a shoulder for a hollow plastic nose which you then tape on with mylar tape. Only problem is where to find such a nose. I think I stumbled on one source the other day...my son and his friends built the Pratt Polaris which uses a T-20+ tube and a vac formed plastic nose. Pratt doesn't sell the nose separately, but buying a pile of cheap Polaris kits may provide a good source for both the tubes and noses needed for this event.
All of this is probably moot, however, until such time as I build a piston.