Thanks for the reply Ron.
I have run across a number of references that call the "ordinance pattern" rifles "Rodmans" -- I assume due to their shape since I find no connection with Rodman and Rodman guns. There is an article in The Confederate Veteran that says Capt. Gurley captured two 3" steel Rodmans at Lexington.
I've been told there are instances where the wrought iron 3" ordinance rifles were referred to as being "steel". This calls into question whether the guns captured at Lexington were actually steel.
The two guns at Lexington TN belonged to Capt. Kidd's 14th Indiana Battery. I've started looking for info on the guns that belonged to that battery and if there is any record that can confirm that they received two or more of the steel Singer Nimick rifles.