Hello Keith:
Thank you for your response and kind words. I welcome the opportunity for questions and discussions concerning civil war field artillery. You raise good points and you have made me aware of my mistake. I completely forgot about the 3" Ordnance Rifle.
Concerning the program to replace the 2.9" Parrott with the new 3" Parrott, yes, they wanted to simplify the ammunition requirements of the artillery service and also, to eliminate any danger of using wrong ammunition in the guns. The 2.9" Parrott was just to close to the 3" Ordnance Rifle for any practical necessity. However, the program to convert the 2.9" Parrott to a 3" Parrott did not proceed as fast as most believe it did. Only on Sept. 23, 1863 did the Ordnance Board adapt a plan to rebore the 2.9" Parrotts to a 3" size. They also recommended about the same time that no more 2.9" Parrotts were to be issued to the field batteries.
The actual order to withdraw all 2.9" Parrotts from service to be replaced by 3" Parrotts was not issued until June 9, 1864. This order was issued by Brig. Gen. George D. Ramsey and yes, the replacement types were to be the 3" Parrott and the 3" Ordnance Rifle. To further cloud the question, 2.9" Parrotts are known to have remained in service, in ever smaller numbers, until the spring of 1865. The production of 2.9" Parrotts ended on April 13, 1863 and the production of the 3" Parrotts began only in February 1864. The 3" Parrotts entered service slowly and this increases the probability that the replacement gun was a 3" Ordnance Rifle.

Concerning the gun carriage used for these guns, the 2.9" Parrott, 3" Parrott and the 3" Ordnance Rifle all used the type 1 gun carriage. The 12 pounder field howitzer also used the type 1 gun carriage and the 12 pounder light field gun (Napoleon) used the type 3 gun carriage.

Finally, after the above, I guess I have to say that I don't known which gun was with the 1st Wisconsin Battery in late 1864. The 3" Ordnance Rifle appears to be the best possibility to be the type asked about, but who knows.

Your Servant
Ron