It seems fairly reasonable that after building ten or so guns using the same frame and bbl. tapers and weight that one could come up with a "close" starting point. I'm sure most true makers have a close idea of where to start. For a one man operation though, it takes so long and you encounter so many unforseen problems that a couple guns are all a man is ever going to do. Even with the best laid out plans, shit seems to happen and it just isn't feasable to start with a real good gun. Here is a 7x57r sauer and you can see how wide the bbls. are at the muzzle. The front ramp had to be that high to get the line of sights right. This is actually the rest of the parts I recently posted.