It's a back action cap lock, and no, it's not a conversion from flint. It was made that way. The back action is an invention a little later than the flint lock era. They are a fraction of a second faster than the traditional lock. I suspect, without seeing the muzzle of your gun, that is a "fowler." That just means it was built as a shotgun for hunting ducks etc.
Another thing, just because J. Bishop is on the lock, does not mean he made the gun, it generally means he made the lock. The gun maker generally had his name on the barrel, and if made in Europe, there would be proof marks on the barrel.
Are you positive it's .69 caliber? Did you measure the barrel?