I developed a good load for the trapdoor cadet at 100 yds., thanks to Larry Gibson. Now I'd like to work out to 600, with a minimum of trial and error firing. Moving a target out in 100 yard increments establishing range dope as you go is VERY time consuming, and increasing weather variables as the day wears on. I want to do a little doping ahead of time with ballistic programs to try to shorten the process. So, I need to estimate a b.c. for my bullet. Now please don't poke fun, my bullet is the Lee 405 gr hollow base, for which I can not find a published b.c. Closest seems to be a Lyman flat base 457193 405 gr, in Cast Bullets 4th Ed they show that bullet at .307 b.c. Those numbers could work, maybe, but I know less than nothing about the effect of the hollow base on b.c....if any. Suggestions ?