I'm not sure what it is, but I don't think it's a Zulu gun. It's a forward lock and the Zulus I've seen are back lock guns. Also the Zulu guns are typically breechloader rifles converted to shotguns.
It's really odd the way the nipple is mounted on the barrel like that instead of having a powder drum. Reminds me of Belgian guns I've seen as well as some early American guns. Also looking at the barrel pic, it looks cut down and the front sight added (it is really far from the end of the barrel which is also odd). Is that a cut off barrel lug, or ramrod guide just past the front sight? The existing ramrod guide seems odd to me as well. I also think the stock has been cut on both ends and possibly the two lock screws have been replaced. I do see what looks like proof marks on the brass side plate, and lock plate those would help greatly in determining a country of origin.
If you can get some close ups of those proof marks I may be able to nail it down, I think I see PG in a rectangle on the side plate, but that one's not on my list. I'll keep looking though. It's a cool old gun for sure.