I've made an assumption that the lock is English, but as indicated by DD's question, there's reason for doubt. I'd like to determine the nationality of this cannon flintlock more definitely. It looks like some other English cannon locks I've seen, but lacks any marking. This general pattern with two transverse holes near the bottom, one of which is slightly elongated, and this shape of brass housing seems fairly common as I've seen several.
One dimension you can't get from the ruler in the photos is the thickness of the brass housing, which is 13/16 inch.
French and Russian locks I've seen are well-marked with the manufacturing arsenal's name. Those are quite different in design from this lock.
I'd like to find photos and/or specifications for American-made flint cannon locks, if any existed, and I suspect they did. Do you know of any specimens, or illustrated references?
Do you know the nationality of the lock pictured, or when this particular variation first came into use?
I've found a few photos of flint cannon locks in Blackmore's THE ARMOURIES OF THE TOWER OF LONDON, V. 1, The Ordnance, HMSO, London, 1976. This lock in general resembles plate 76, item 265, "Ashton's Percussion Conversion Lock" but differs in some details. The Ashton lock shown as item 265 is a simple percussion conversion of an existing British flintlock.