A bullets accuracy starts at the base and moves forward. I think that a lot of the problems (not all) when dealing with boat tale bullets are found in the barrels crown. In my experience I have found that a perfect crown on a barrel is critical to the accuracy potential of both the rifle and the bullet. With a boat tail design the effect of a poor crown is amplified. When the gas escapes on one side of the boat tail first it will cause a bullet to "yaw" a bit before it completely stabilizes. The gasses hitting the angled base will force the bullet to yaw. Barrel "whip" also contributes to bullet yaw to an extent. H-BAR is right when he says "Flat base bullets are easier to make shoot accurately at short range," The key word is "easier," due to their design. Consistency is everything when talking extreme accuracy and of course the faster you can get a bullet to stabilize (any bullet) the better off you are.
Good hunting.
Q,