Miller, as I recall, the 7 D has the boxlock action. I have not checked the O Excelsior. Off the top of my head, I do not remember how to tell without removing the trigger plate... something else I need to check out. If you have Robert Elliot's second book, "Uncle Dan Lefever- Master Gunmaker", the cocking mechanism of my 7 D is shown in the top photograph on page 98.

The inner workings of my 7 D were also pictured in a Double Gun Journal article by Keith Kearcher. I would have thought this gun never had a screw turned until I saw it partially disassembled in that article, and recognized the very low serial number. Just goes to show what is possible with correct hollow ground screwdrivers and good technique.