Model 1868 I just found at a yard sale...

[Fred]

I think Chuck may have come up with the answer - it would probably be possible to measure whether ALL of the impact centers fall within the range of a bounced rod; if they do I'd bet that's it. The block face should be hard, too, though. Also, remember that these were essentially test guns - maybe it was a controlled experiment at the Armory to see what kind of abuse the block would stand? Somewhere I have seen instructions warning that the soldier was NOT to "spring" the rod in the bore, but do not recall the exact time-frame, or specific model. Best part about it is that the "damage" is totally concealed and can be exhibited (or not) at your option.

I don't know if anyone can tell, but I coated the back end of the rod with oil and then brought it into repeated contact with the breech block face to see how well the dents matchup with where the rod made contact with it. It's a match. So, as we suspected, the damage was indeed caused by the tip of the small end of the cleaning rod. Quite possibly it was indeed a test of some sort on this rifle.