Someone has attempted to "improve" the gun by cutting off the fore end, and adding a rib. If it is straight rifled, it PROBABLy was originally full stocked. It could have been half stocked, with the nosecap just ahead of the lower rod pipe, but it definitely was not made with a rib.
![Wink ;)](https://americanlongrifles.org/forum/Smileys/default/wink.gif)
And the straight rifling is NOT for collecting fouling (an old shooters' wives' tale), it is for stabilizing shot.
Nice gun, though, mid 18th century or so (the butt is pretty narrow, which makes me think it's later). It was definitely originally flint.