This is a Sharps New Model 1863 carbine that was later converted to metallic cartridge. The US Government had approx 30,000 of these carbines converted to 50-70 Government, and refer to these as the US Model 1868 Sharps Carbine. These saw heavy western use amongst US Cavalry units.
Many percussion carbines were also owned / converted to metallic cartridge in the 1860s - 1880s. To see if you have a Government conversion or a civilian one, see if you can make out a government cartouche on the left side of the buttstock - should find "DFC" in a banner for David F Clarke - government inspector.
May be a rebarrel or may be lined. Finish of the barrel is often slightly bluer than the case coloured receiver which often greys out over time.
Value wise these tend to go for the 2500-3500 range up here in Canada from my experience.