This is indeed a very unusual query. It leads to many questions arising in one's mind. Leaving aside the legality part, why do you want to bring in a deactivated gun to Qatar? How will you be able to bring it in? To my knowledge, airlines wouldn't accept it even as cargo. Then, what are your "intentions"? A deactivated gun can be activated with specialist tools and skills.
I know it is getting a pretty cold in your part of the world and you really need the warmth of Qatar to allow your mental system to function well.