Hello Ken,
These guns are Singer-Nimick 3" steel rifles made in the same profile as the M1861 Ordnance Rifle. Incidentally, the Singer-Nimick guns are also model M1861. It was and still is quite common for artillery pieces to be mis-identified by soldiers in the Civil War and presently even by experienced re-enactors. You have to filter through these wrong identifications. These guns are Not Rodman's. The smallest gun or rifle made by Rodman was 8" in bore. So, to call them a Rodman is wrong. I try to a purist in identifying artillery pieces but it is not easy.
Thanks for your questions about artillery. Wish we had more.
Ron