According to Flayderman's Guide, this is one of only approximately 50 of these early variant Cosmopolitan carbines with the double loop enclosed lever with the locking latch located inside the rear loop. This is the predecessor to the "contract type" Cosmopolitan carbines which were manufactured from 1859 to 1862, and then the Gwyn and Campbell marked carbines manufactured between 1863-1864; both of which saw use in the Civil War. This rare Civil War carbine was manufactured by the Cosmopolitan Arms Company of Hamilton, Ohio. The company was owned by E. Gwyn and A.C. Campbell. Lock plate marked "COSMOPOLITAN ARMS CO/HAMILTON.O. U.S/GROSS' PATENT" and faint remnants of Cosmopolitan Arms Co. markings on top of the frame. Matching serial number "57" marked on the bottom of the barrel and frame, and on the breech block.