I've been pondering your yaw illustration, which I know is exaggerated.  What I'm thinking is fill up that space around the boat tail with powder. It'll be there, under pressure, even when the neck is expanded, and as the bullet travels through the neck and starts into the throat.  That should further minimize any chance of yaw.  I can think of a few slow burning ball powders that ought to do that, Norma MRP or Hodgdon's Superformance.  Those suggestions are for those of you who can afford them.  Me, I have some dirty burning WC860 to play with.  I wish I had quickload to play with, it'd be interesting to see what those ball powders would do with a 174gr bullet out of a 30" barrel.  They'd likely need to be fired with magnum primer to get the most out of them, at Krag pressures.