I assume it's a Spencer Rifle . . . wish you had told me to be sure. There are two Choices based upon the serial # you gave me - #7670. Closest serial #s I found are:
Spencer Rifle Serial #s 7654 & 7669 were issued to Company B, 8th Indiana Volunteer Cavalry (NO Date Listed)
Spencer Rifle Serial #s 7678 & # 7684 were issued to Company E, 11th Ohio Volunteer Cavalry on August 21, 1863.
Best I can give you . . . hope this is of some help. Hope you read my Serial Number Disclaimer on the SSS Home Page.
Two Flints