Quote:
Originally Posted by zombietactics:
You're confusing the formula for the area of a circle (A = пr²)  which was never in doubt or even a question, BTW ... with crosssectionalarea: ....but I'm through quibbling.

Sure, toss in the towel when you are called on something that you cannot "walk back".
The crosssectional area of an expanded round is best described as being that of a circle.
Of course, we could go one step further and compute it as the surface area of a partial, oblate sphere, but the difference is trivial in practice and not worth the trouble. You can try to walk it back all that you want, but the fact remains that you said
Quote:
Originally Posted by zombietactics:
Brief primer: diameter is a meaningless measurement for the problem, crosssectional area is more to the point.

and crosssectional area (the dimension you've chosen to hang your hat on) is determined by the diameter (or the radius) of the expansion face (which is typically circular (or slightly stellate that is, shaped like a star) and has an area that is best described by A = пr². That surface area, BTW, has a profound effect upon the way a bullet decelerates within a medium (through viscous and inertial drag forces) so it is very important in the consideration of the problem at hand terminal ballistics.