For the siege of Fort William Henry, I have never seen a "true" inventory of the guns. We have a excellent inventory for October 1756, but not August 1757. We know that in October 1756, there were 35 artillery pieces at Fort William Henry. At least six 18-pounders, two howitzers, and one 13-inch mortar were stripped from Fort William Henry and moved, the math and later descriptions suggests they were moved to Fort Edward. I find it interesting that no "history or book" on the siege has picked up on that point (buried in letters from Loudoun to Cumberland).
My guess is at the time of the siege, there were a total of 25 pieces. This total number is in good agreement with several Osprey publications, but the current Osprey texts all lack a breakdown of the inventory. My guess at the artillery:
2 32-pounders
2 18-pounders
3 12-pounders
5 9-pounders
4 6-pounders
4 4-pounder
1 Howitzer (7 1/2 inch)
4 Large Mortars (some 7 1/2 inch - maybe some 10 1/2/ inch)
The "official" report on the Siege at Fort William Henry had been unknown for over two centuries, but was found buried and forgotten in the Lord Loudoun Papers housed at the Huntington Library by Ian Steele. It is the only known copy of the document. Unfortunately, Steele did not find it until after his book "Betrayals: Fort William Henry (1990)" was published. This "official report" was published in the Huntington Library Quarterly, 1992. In this document, there isn't an inventory of guns at the start of the siege, but there are lists of guns remaining 4 or 5 days into the siege, guns surrendered to the French, and some comments on losses due to "bursting". The numbers in this report do not agree with the "Fyre journal", which really isn't a journal, but a report written to the Governor of Massachusetts about 1 or 2 months after the battle. The two 32-pounders and the two 18-pounders are very solid.
Very interested in seeing what the new Osprey text will say on the artillery inventory, scheduled for release in Fall 2013.
Plus 17 swivel guns
I will have to look up the french artillery inventory tomorrow, but I would think the largest guns were 16-pounders, but with a decent number of large mortars. The french had more guns total than the British. For 2 or 3 days, the British had the freedom to shoot at the French, without the French being in position to respond --- the French were still digging trenches and their first series batteries were not completed. During this "free to shoot at the French" phase, the British burst their 4 largest guns and several of the largest mortars. By the time, the French opened their first artillery battery, the largest gun remaining to the British were the 12-pounders plus they might had had 2 large mortars remaining. Apparently, the British lost only 1 gun to direct fire by the French, a 6-pounder. The howitzer and the four 4-pounders were among the guns surrender to the French. By the end of the siege, all the British mortars were lost to bursting.