George,
I understand the theory behind that, but some things just won't work out just right without some known dimensions to go from, ie. lock plate, buttplate, triggerguard, barrel length, width at breech, etc.
Gives some place to start to get the enlargement ratio.
Also, some areas are not shown, like from above looking down, for wrist dimensions, breech width, etc.
Just trying to get as much info as possible before I start.