Looks like a 1855 Sidehammer or "Root" revolving rifle. He may have been killed by his own weapon. Those things scare the dickens out of me due to chamber firing. Great way to lose a hand and bleed out of the field. If you've ever experienced a chamber fire you will not want to do it again. Been there and done that! Thank goodness it was only blank charges and powder burns to my elbow instead of the loss of a hand..