Good luck with that rifle. I've yet to see any of these tight chambers preform consistently well.
Doing the chamber cast is probably a good idea, just to make sure about the chamber measurements.
If you can't get that 434470 bullet cast from 16-1 and wrapped in 7 lb paper , on top of 76 grs of OE 1 1/2, to shoot well then you may want to consider having some one open that chamber up.
