That "Pre-Breech" notation on the crossbolt Wedge/Key is a bit confusing. With the metal portion of the forend iron showing this certainly looks like a breech loader to me. Certainly this was a common method of securing the barrels & stock together on muzzleloaders but it also carried over to the forend of early breech loaders. My Ca 1863 W & C Scott bar in wood pinfire has the forend attached this way.

Miller/TN
I Didn't Say Everything I Said, Yogi Berra