Something I've been pondering, Rory, is length of bearing surface in relation to overall length of the bullet in this application. I wonder if a .25 bullet that's theoretically short enough to stabilize but has an inordinately long bearing surface (think, say, a 100+ grain bullet with a very blunt round nose and not much of an ogive) would or wouldn't stabilize. Someone asked me that recently, maybe Joe, and I couldn't come up with a definitive answer.
