Originally Posted by 5.56X45mm

Yeah, mmarsh hit the nail on the head. It's a 1856 Enfield Rifle-Musket. It's a .58 Caliber Rifled Musket. Uses Percussion Caps as a way to ignite the powder. Seems to be in okay shape. Take it to a gun smith and have him look it over and get it cleaned up. You have some major pitting on the hammer and nipple. It's not going to be a pretty gun but it might still fire once it's all cleaned up. Most of the rust appears to be surface rust.

Side note about your rifle. It might be Confederate. During the War of Northern Aggression. England supported the south and sold them arms. The 1856 Enfield Rifle-Musket was one of the most common issue weapons for the Confederacy.