I will try to give some insights as to what pieces were generally fielded in what quantities during the Seven Years War.At the beginning of the 18th C., French military authors advised a ratio of 1 piece per 1.000 combatants. This ratio seemed to have remained rather consistent – more or less – till well into the Seven Years War. Only the introduction of the Swedish-style light 4-pdr bataillon guns as per the Royal Ordonnance of January 1757 increased the ratio of gun per combatants somewhat.
Detail from a series of paintings with scenes
of the War of Austrian Succession by Nicolas van Blaremberghe
painted between 1778 and 1790.
The field artillery of the 1748 royal French army of Flandres consisted of 14 16-pounders, 16 12-pdrs., 30 8-pdrs., 80 ’long’ 4-pdrs, and a reserve of 10 Swedish-style short 4-pdrs. (at that time not employed as bataillon guns) – or a total of 150 pieces for an army of approx. 114.000 men (See: Ernest Picard, L'Artillerie Française au XIIIe Siècle, Paris & Nancy, 1906; also Guillaume Le Blond, L‘Artillerie Raisonnée, Paris 1761).
The French army of the Weser in 1757 under maréchal d'Estrées' fielded some 100 pieces for approx. 100.000 men, not including the bataillon guns. A more detailed break down could not be found. However, the marquis de Valfons, chief of staff to general Chevert, gives a record of the heavy artillerie brought into action by general de Vallière on the heights of Hastenbeck a day before the battle as the French army was filing into its position. He notes Vallière managed to deploy 30 pieces of 16 and 12-pounders as well as 4 24-pounders for the bombardment of Cumberland's position on 25 July (see: Souveniers du marquis de Valfons, Paris 1860).
Really, different to other nations artillery organisation of the period, the French did not distinguish between siege and field artillery. If thought fit, the entire range including the heavy 16 and 24-pounders would serve as field artillery.
Maréchal Contades army of 1759 accounted for 14 12-pounders, 32 8-pdrs., 66 4-prds. longues, and 6 howitzers (8 inch) – or a total of 118 pieces, not including those of general Armentières Lower Rhine army. Source is an original schematic order of battle dated July 1759 found in prince Ferdinand's archive. No word here on any 16-pounders, but there is indeed fragmental evidence some had seen action at Minden. ‘14-pounders’ are said to have been captured that day and were incorporated into the Allied army's artillery train. Young lieutenant Hugh Montgomery of the English 12th Foot mentions in a letter to his mother his regiment came under fire of a battery of ‘18-pounders’. Possibly this has to read more rightly 16-pounders in both cases.
We have also record of maréchal Broglies' army of Hesse in 1760, thanks to the Allied army's efficient intelligence. Around 22 June with the commencement of the summer campaign, his heavy artillery consisted of 24 12-pdrs., 32 8-pdrs., and 6 ‘16-pdr’ howitzers (would equal approx. 6.5 to 7 inch class – possibly captured Hannoverian ordnance, for French only fielded 8 inch pieces during this period to my understanding ?!?). Total was 110 pieces for his army of approx. 138.000 men. No mention of 4-pounders here, but Broglies instructions for this campaign reveal each of his army's 6 columns or divisions (4 of infantry and 2 of cavalry) were to have each 8 pieces or a total of 48. Voilà, that adds charmingly to the afore mentioned 110 pieces (see: C.H.P.E. von Westphalen, Geschichte der Feldzüge des Herzogs Ferdinand von Braunschweig-Lüneburg, vol. IV, 1859-72). Again no word of any pieces of over 12-pdr weight, but we know 4 16-pounders were fielded at the battle of Kloster Kamp 16 Oct. 1760 as part of the French advance guard under general Chabo.
Summarising the above details, it can be said the greater part of the French position artillery was made up of long 4-pdrs. and a good number of 8-pdrs. during this period. 12-pdrs. would have been fielded in much fewer numbers, and also the heavy 16 and 24-pdr. cannon did see employment in battle.