Webmaster advised what the problem was so here is a modified answer. The photos, description and serial number all point to this being a M1860. The carbines were produced in a serial number range of 11000 to 61000 so this one fits. This one seems to be a candidate for issuance, likely toward the end of the conflict (last year.)

Springfield Research is undergoing some changes but claims to be planning to be back up in a few months. I think--emphasis on think-- that you can contact them with the full serial number and if it is in the database, they will issue a letter with what information they have on hand. I could be wrong about this.

Good luck.