Jim,
The barrels looked very rough but when I ran a patch no pits and lots of red rust.
Barrels are 29 1/8 " long and do not appear to have been cut as they muzzles are touching. I will get some more pictures in a few days. I have sent a note to a Heckenback family website to see if they have any information. He later became a doctor and practiced in Chicago.

Here is the patent specification


Patent drawing


Cheers,
Laurie

falling block