devisser aka/ RFD,
Please read my disclaimer
Some time ago I acquired the four volume set of the Springfield Research Service (SRS) Serial Numbers of U.S. Martial Arms. I purchased the set so I could help SSS members identify which unit their original Spencer Carbine or rifle was issued or assigned to during, and perhaps, after the Civil War.
Unfortunately, not all the Spencer serial numbers are listed in the four volume set I own. And, there are gaps between indicated serial numbers. This paragraph is a DISCLAIMER of sorts. As a courtesy to SSS members, I am happy to reveal to you the information I have regarding the serial number of your Spencer carbine or rifle. But, please remember, I am just regurgitating what I read in my SRS volumes with some "unscientific conjecture" on my part . What I do is the following: I take your Spencer serial number and try to place it in between the two closest serial numbers to yours listed in my SRS volume. In most cases, if the serial numbers for the Spencer before and after your own serial number were issued to the same unit, I assume your Spencer went to the same unit. Or, if your Spencer serial number is very, very close to another Spencer serial number, I assume your Spencer went to the same unit. I call this the “Two Flints guesstimation”). I’m guessing and estimating at the same time on what I believe to be correct information based upon the information I find in my four volume set of SRS. If the information is lacking in correctness and or accuracy, it ain't my fault. I'm just doing the best that I can do with what I have to work with. And that is the best that I can do for you.
Having written all the above, regarding your Spencer Carbine serial # 12484: Nearest match to your serial #12484 I have is #12465. Your Spencer Carbine may have been issued or re-issued to a member of Co D of the 6th Illinois Volunteer Cavalry in 1864.
Two Flints