If any of you want to look at the "big picture" dealing with ballistics go to the following link
http://www.fas.org/man/dod-101/sys/l...fm6-40-ch3.htm
It contains the FM 6-40 Manual Field Artillery Gunnery. Although it discusses items on a Macro scale, it is a good primer for the discussion of ballistics.
Oh- If the greenhill formaula is a extraction from research done by artillerymen, be aware of the fact that standard condition, as computed by BRL at Aberdeen, for artillery systems are different than their computed standard conditions for small arms.
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God truly fights on the side with the best artillery