Nice so far!

I think they often have a hole in the side where you load the shells in, and a kind of slide that pushes up towards the barrel to lock them in, or the actual gun snaps open and they load from the back, as in this image.

Couldn't find one quickly that showed the side loading, hope you get what I mean though.

Actually, just realised the hole on the side is where the shells eject from after firing, it seems they can be loaded from an actual magazine though, like a rifle, just infront of the trigger on the underside.