It appears to be one of the US muskets...circa 1840's-1850's...Springfield, maybe Enfield...just can't tell much from only two pictures. It does look like it has been badly modified of the years which also makes identification tough. One thing for sure, it is NOT a Trapdoor or any other cartridge gun. It is clearly a percussion gun. It is pretty hard to give much help with just those two pictures to go on. Take it to a gun show and I am sure there will be someone that can make a positive ID on the old girl.