Gary, here's what I've read not what I know: Flatbased bullets tend to be more accurate than boattailed bullets simply because it's easier to make the base of a flatbased bullet nearly perfect. If the base of the bullet releases gases unevenly, the bullet will be deflected as it exits the barrel. However, if the base of a boattail is as good as the base of a corresponding flatbased bullet, then the boattail will tend to be more accurate than the flatbased bullet because it has a higher BC and will be deflected less by minute changes in the wind. (Since the shape of the ogive also affects BC, this assumes that the two bullets have the same ogive.)
Having a higher-BC bullet can help at any range, it just depends on the conditions. If it's a relatively calm day, the difference between the two might be too small to notice. But, as the wind picks up, you'll start to notice less deflection with the higher-BC bullets.
As to the effects of longer bearing length, I've never seen anyone suggest that a longer bearing surface makes a bullet more accurate. It could reduce in-bore yaw as 303Guy suggests, but I kind'a doubt it. There's enough force behind a bullet to swage a bullet into just about any shape, so I don't think it could help realign something that it out of alignment, but I don't know for sure. I do know that the long-range BR guys sort their bullets by bearing surface to ensure that they only shoot groups with the same length bearing surface.
I don't think round-nose bullets are more accurate than others. My only evidence for this is that if they were, every short-range BR guy in the world would be using them. If one guy started winning matches with a round-nose bullet, at least half of them would switch bullets overnight.
There's a lot of "think" and "tend" in this reply, but from what I've gathered no one really knows the answers to questions like this. The only facts seem to be statistical correlations of results. About the only thing that seems to be known for certain is that different barrels like different combinations of components and you need to use the one that works.
robert
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