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I have found that even bullets leaving the barrel at EXACTLY the same speed but having as little as .002" difference in bearing surface length can yeild as much as a minute and a half impact variation!
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Great post! I'm guessing it's even worse than you suggest as a longer bearing surface (BS) would have more friction and yield a lower velocity. If longer BS increases BC the effect may be somewhat ameliorated (but my guess is the longer BS would lower
Here is a pic of my set up. Dual Banjo's -- oops Dual SP
Bullet is a 190gr SMK .308
Not that I need to do this right now given my longest kill (717 yards) is exactly one mile behind Kirby, but I'm getting ready.