Digby,

I did a closer examination of the illustrations that come with the Favé book "Études sur le passé et l'avenir de l'Artillerie.
In case you intend to do an illustration. The metric scale he added is faulty. The barrel is really only approx 17 calibres length, not 18.
Favé confuses length of soul/bore with barrel length. He also confused this with some of the Prussian 1740's ordnance he talks about before or after. The true dimensions are found in St Remy edition 1745 that includes also a table with all mesurements. Somewhat cryptic, for the column giving the feet is missing. Only inches and lines can be seen. But the feet dimensions can be scaled with ease, I should say.

Cheers,
Christian