Brent,
The "lump" looks like the bottom of a side lever.
I also think you would have a better chance of dating the photo by the man's shoes or apparel or even his mustache than by the gun. I'm sure there are still gentlemen out there hunting with a sidelever hammer to this day. I'm not certain we could say he was hunting with a gun that was brand new that year, right?
I'd also like to spitball and say the horn insert in the forend would make this gun from Europe. But again, just a guess. I'll be interested to hear what others know/think.
