Hi
Another problem that can have an effect on accuracy is that some cylinder chambers are in fact undersize compared to the bore diameter so that when you load the balls you can shave to much off and it doesnt grip the rifling properly.
Ive never checked this myself just read about it on another forum where the guy made a chamber reamer so that the chamber was opened up to a couple of thou larger than the bore or as close to the correct bore size as possible.
Peter