It probably wouldn't be flush with his wrist, or the rest of his gauntlet of that's what you were wondering, it'd be pretty easy to attach a weapons platform to the top of his wrist. It would kind of look like the contraption on that gi Joe, except instead of a pair of gatling guns, it'd just be a single barrel with a 5 round magazine. 

Of course, for all that trouble, a pistol would probably be more practical. I just like the idea of wrist weapons