Pinning the join is a wise idea. A simple butt join--two flat surfaces butted up against one another--is not as strong as a join with a pin inserted into holes drilled into the mating surfaces. Not only does the pin supply additional strength, perpendicular to the mating faces, but it increases the area to be glued.
Superglue, better known as CA (cyano-acrylate) glue, if you got to a hobby shop, is pretty good, but I've been using 2-part epoxy glue more and more, because it's stronger in the long run. CA glue can become brittle, over time.
In this case, is the rifle held in the figure's hand, and is the hand cupped/curled to fit around the rifle? In that case, then CA glue should work pretty well on its own.
As an aside, we might want to move this thread to the Model building subforum; "Forum How-To's" is really for usage questions about the forum itself, such as how to upload pictures, how to edit my signature, and so on.
Prost!
Brad