Digby,

I'm currently pushing on with my illustrations of 7YW ordnance. Have done a good deal of reading.
Your question, I'm sure, will end up in tedious studies of a lot of nonsense. It seems, there were many systems circulating and everybody laboured about by following his best asumtions. For most part it was no more then that, plus a series of tests that would not be entitled this way by todays standards. That is to say, results should be regarded as for most part as random.
If you are interested, I can provide you with copies of a rare paper by Hans Bleckwenn on Prussian 7YW arty titled "Die preußischen Feldgeschütz-Typen 1756–1762 in Beziehung zur allgemeinen Gefechtstaktik" puplished in the German periodical Zeitschrift für Heeres- und Uniformkunde in 1958.
A good starting point as it lightens the different concepts or understanding of what should be demanded from this arm.
He makes a short summery on how and why they arrived at their considerably lightened pieces – and from 1759 on returned back to more heavy or solid pieces). All important for what I take to be the "true story". It caused the Austrians to follow suit (Liechtensteins observations at the battle of 1742 Chotusitz being the key here).
French just followed suit. It all starts with Prussia - not true. Better said with the Swedes and the gradual adoption and augmentation of light field guns in the line of battle that required to be manhandled. I believe this to be a Nordic Wars sort of learnings early 18th c. Prussia then gave the Austrians a learning from 1741 on, and sometimes later the news also spread across the Rhine. Doing lengthy studies of ballistics won't get you very far, I fear.
I learned, French cannon manufacture wasn't all that good till about mid 18-hundreds. Best founders were usually found in Germany. See 1734 siege of Phillipsburg were many pourly cast French barrels simply fell apart during action. The Swiss Maritz founders innovations from mid-18h improved a lot here and may have given theM1732 Vallière and the post 7YW Gribeauval pieces a slight edge in quality from, say, 1750 upwards, but hardly anyone at that time would have noticed.I'm inclined to say not even an 1806 Prussian Jena veteran would have observed a superiority of French guns in terms of superior casting or design. The Maritz founders, of course started working in France before 1750, but only gradually, the old pre 1732 ordnance would have been replaced. At this time, I'm inclined to assume that even by the 7YW not all French pieces fielded were 1732+ casts. Possibly also older ordnance was fielded.
Let me know if you are interested in the Bleckwenn paper.

Cheers,
Christian