Well, here's the gun in detail. I pretty much know the answer, but you let me know for sure before I change it.
It's a .44 mag/16 gauge LeMat revolver mechanism built into a custom frame. It holds 9 rounds/ 1 shell
So the mechanism on the top with the barrel and handle style on the bottom. Chromed with black grip. Both barrels would be inside the black bar there.
Spoiler (click to show/hide):
Clearly, I haven't actually tried to build this monstrosity, but I'm taking things like ammunition sizes from the specs of LeMat's that have been made before. I'd just as happily make it a .38 special and it goes without saying that I won't be starting with magnum/special ammunition.
(Don't give me that look. I can know stuff, too. I researched the hell out of this thing years back for a character and it's been kind of a reoccurring weapon for me ever since.)