Ah, there we go... Didn't see the attach file icon before :P
When I took a look at the firearm last weekend, I noticed that it was a smoothbore, and not rifled. And I can tell you that I am fairly certain my bore measurement was wrong (only had a piece of graphpaper at the time)
I'll give my G-pa a call today, see if i can get more accurate measurements on the length and bore.
I wouldn't be surprised if it is a replica, and while a little disappointing, it would make it more likely that the weapon is taken to a range and used after we get it cleaned.
I do appreciate the comments and the help.