Dr. Tim Boone,
I must apologize for a mistake. I reexamined the photos and found the missing proof mark hidden in the rust on the breech tang. Because that proof is there (The Perron which depicts the Tower of Liege) these barrels would have been from sometime after 1853 and before 1877. And they would also have been appropriately proofed in the Govt proof house. The proof load would have been 2/3 of the ball weight in powder under a single ball with a paper wad above the powder, then the ball, followed by a second paper wad. The proofs would further indicate they were most likely made for export as raw barrels because otherwise there should be additional proofs. Despite proofs being a matter of law, many variances appear in violation of the procedure (guess their government is no more accurate/reliable than ours.)
There is another proof mark on the lug which is too obscured by rust to be readable. If I could determine what that mark is, it is possible we could identify the maker or perhaps the inspector which would more accurately date the barrel's source or age.